The role of low-fat diets and fat substitutes in body weight management: what have we learned from clinical studies?

Switching from high-fat diet to normal diet ameliorate BTB integrity and improve fertility potential in obese male mice

Obesity is a prominent risk factor for male infertility, and a high-fat diet is an important cause of obesity. Therefore, diet control can reduce body weight and regulate blood glucose and lipids, but it remains unclear whether it can improve male fertility and its mechanism. This study explores the effects of switching from a high-fat diet (HFD) to a normal diet (ND) on the fertility potential of obese male mice and its related mechanisms. In our study, male mice were separated into three groups: normal diet group (NN), continuous high-fat diet group (HH), and return to normal diet group (HN). The reproductive potential of mice was tested through cohabitation. Enzymatic methods and ELISA assays were used to measure metabolic indicators, follicle-stimulating hormone (FSH) levels and intratesticular testosterone levels. Transmission electron microscopy and immunofluorescence with biotin tracers assessed the integrity of the blood-testis barrier (BTB). Malondialdehyde (MDA), superoxide dismutase (SOD), and reactive oxygen species (ROS) were inspected for the assessment of oxidative stress. The expression and localization of BTB-related proteins were detected through the immunoblot and immunofluorescence. The mice in the high-fat diet group indicated increased body weight and epididymal fat weight, elevated serum TC, HDL, LDL, and glucose, decreased serum FSH, and dramatic lipid deposition in the testicular interstitium. Analysis of fertility potential revealed that the fertility rate of female mice and the number of pups per litter in the HH group were significantly reduced. After the fat intake was controlled by switching to a normal diet, body weight and epididymal fat weight were significantly reduced, serum glucose and lipid levels were lowered, serum FSH level was elevated and the deposition of interstitial lipids in the testicles was also decreased. Most significantly, the number of offspring of male mice returning to a normal diet was significantly increased. Following further mechanistic analysis, the mice in the sustained high-fat diet group had disrupted testicular BTB integrity, elevated levels of oxidative stress, and abnormal expression of BTB-related proteins, whereas the restoration of the normal diet significantly ameliorated the above indicators in the mice. Our study confirms diet control by switching from a high-fat diet to a normal diet can effectively reduce body weight, ameliorate testicular lipotoxicity and BTB integrity in male mice, and improve fertility potential, providing an effective treatment option for obese male infertility.

Influence of betahistine repeated administration on a weight gain and selected metabolic parameters in the model of excessive eating in rats

It is important to search for a promising therapeutic target or small molecules that can control excessive eating since limiting the intake of foods, especially tasty ones, could be effective in the treatment or prevention of obesity. Some studies indicate betahistine as an unique drug having the ability to ameliorate, for example, antipsychotic-induced weight gain. This study aimed to determine whether repeated administration of betahistine (histamine H1R agonist and H3R antagonist) could be beneficial in reducing the intake of tasty foods or the body's response to overeating via mechanisms such as by influencing the levels of hormones involved in the regulation of food intake or the levels of selected metabolic parameters. Studies were performed in the excessive eating model in rats, which perfectly illustrates the harmful high-caloric intake from freely available tasty products rich in sugar and fat. Our results indicated that repeated administration of betahistine to rats caused lower gain of body mass compared to the control rats fed palatable feed. Interestingly, betahistine treatment increased the consumption of cheese, which is a source of histamine. Although betahistine did not prevent the development of metabolic disorders, such as reduced glucose tolerance, in test animals, it significantly increased the level of high-density lipoprotein cholesterol, which could certainly be considered beneficial. Further studies should be conducted to investigate the effect of repeated administration of betahistine on satiety, gastrointestinal disorders, and the preference for histamine-containing foods.

Pleasure junkies all around! Why it matters and why 'the arts' might be the answer: a biopsychological perspective

Today's society is pleasure seeking. We expect to obtain pleasurable experiences fast and easily. We are used to hyper-palatable foods and drinks, and we can get pornography, games and gadgets whenever we want them.

THE PROBLEM

with this type of pleasure-maximizing choice behaviour we may be turning ourselves into mindless pleasure junkies, handing over our free will for the next dopamine shoot. Pleasure-only activities are fun. In excess, however, such activities might have negative effects on our biopsychological health: they provoke a change in the neural mechanisms underlying choice behaviour. Choice behaviour becomes biased towards short-term pleasure-maximizing goals, just as in the addicted brain (modulated by the amygdala, posterior ventromedial prefrontal cortex' (VMPFC), striatum, nucleus accumbens; 'A-system') and away from long-term prosperity and general well-being maximizing objectives (normally ensured by the insula, anterior VMPFC, hippocampus, dorsolateral prefrontal cortex (DLPFC), anterior cingulate cortex (ACC); 'I-system'). This paper outlines, first, what 'pleasure' is and what 'pleasure-only' activities are (e.g. social media engagement, hyper-palatable eating). Second, an account is given of the type of action that might aid to maintain the neural systems underlying choice behaviour balanced. Finally, it is proposed that engagement with the arts might be an activity with the potential to foster healthy choice behaviour-and not be just for pleasure. The evidence in this rather new field of research is still piecemeal and inconclusive. This review aims to motivate targeted research in this domain.

Adipose tissue metabolism and inflammation are differently affected by weight loss in obese mice due to either a high-fat diet restriction or change to a low-fat diet

Restriction of a high-fat diet (HFD) and a change to a low-fat diet (LFD) are two interventions that were shown to promote weight loss and improve parameters of metabolic health in obesity. Examination of the biochemical and molecular responses of white adipose tissue (WAT) to these interventions has not been performed so far. Here, male C57BL/6JOlaHsd mice, harboring an intact nicotinamide nucleotide transhydrogenase gene, were fed a purified 40 energy% HFD for 14 weeks to induce obesity. Afterward, mice were divided into three dietary groups: HFD (maintained on HFD), LFD (changed to LFD with identical ingredients), and HFD-CR (restricted to 70 % of the HFD). The effects of the interventions were examined after 5 weeks. Beneficial effects were seen for both HFD-CR and LFD (compared to HFD) regarding physiological parameters (body weight and fat mass) and metabolic parameters, including circulating insulin and leptin levels. Macrophage infiltration in WAT was reduced by both interventions, although more effectively by HFD-CR. Strikingly, molecular parameters in WAT differed between HFD-CR and LFD, with increased activation of mitochondrial carbohydrate and fat metabolism in HFD-CR mice. Our results confirm that restriction of the amount of dietary intake and reduction in the dietary energy content are both effective in inducing weight loss. The larger decrease in WAT inflammation and increase in mitochondrial carbohydrate metabolism may be due to a larger degree of energy restriction in HFD-CR, but could also be due to superior effectiveness of dietary restriction in weight loss strategies.

Different dietary strategies for weight loss in obesity: role of energy and macronutrient content

Obesity is a chronic disorder caused by an imbalance of the energy metabolism with high associated burdens. Therefore, huge efforts are being currently devoted in studying new types of hypoenergetic diets and their composition, in order to characterise more specific, long-lasting and safe slimming protocols. A number of investigations are trying to determine the specific influence of the macronutrient distribution in energy-restricted diets on the management of excessive body weight. In this context, very-low-energy diets supplying between 1670 and 3350 kJ (400 and 800 kcal)/d have been beneficial in short-term treatments causing a weight loss of 300-500 g/d. Such strategies place more emphasis on energy restriction than on the macronutrient composition of the diet prescription. Weight loss produced by either low-carbohydrate or low-fat moderately energy-restricted diets ranges from 0.5 to 1.0 kg/week, while diets with high or moderately high protein content have also been applied in weight-reducing programmes by inducing losses of 0.2-0.4 kg/week. Other factors that determine weight loss by dieting are sex, age, initial body weight, race, genetics, regional fat deposition, etc, which must be taken into account to explain the variability in the outcomes of different low-energy diets. Therefore, more research is needed about the impact of diets with different fuel substrates and foods on the characteristics of the weight-loss process.

[Impact of a lifestyle intervention program on metabolic, anthropometrical and dietary profile of Japanese-Brazilians with and without metabolic syndrome]

OBJECTIVE

We evaluated the changes in biochemical and nutritional profiles of Japanese-Brazilians with and without metabolic syndrome after two years of participation in the intervention program.

MATERIALS AND METHODS

It was a non-controlled experimental study. The biochemical and clinical assessments were conducted at baseline (2005), after a year (2006) and after two years (2007) of intervention. On the present study, data of 360 individuals, who participated on the three assessments were considered.

RESULTS

Both groups presented improvements on the anthropometric and metabolic profile, after two years of intervention. It was observed reduction in the intake of total fat, saturated fat, and dietary cholesterol, and increased intake of fiber among men without metabolic syndrome. It was observed reduction in the intake of total fat (p = 0,003) and monounsaturated fatty acid (p = 0,002).

CONCLUSION

The results showed a positive impact of the lifestyle intervention program in metabolic and nutritional profile of Japanese-Brazilians with and without metabolic syndrome.

Low-fat dietary pattern and change in body-composition traits in the Women's Health Initiative Dietary Modification Trial

BACKGROUND

The Women's Health Initiative Dietary Modification (DM) Trial was a randomized controlled trial that compared the effects of a low-fat (≤20% of total energy) or a usual diet in relation to chronic disease risk in postmenopausal women.

OBJECTIVE

We characterized long-term body-composition changes associated with the DM trial and potential modifiers of these associations.

DESIGN

In the DM trial, 48,835 women aged 50-79 y were randomly assigned to intervention (40%) or comparison (60%) groups. We studied a subset with whole-body dual-energy X-ray absorptiometry scans at baseline and during follow-up. Changes in fat mass (FM), lean mass (LM), and percentage body fat between the intervention (n = 1580) and comparison (n = 2731) groups at years 1, 3, and 6 were compared. By using generalized estimating equations, we calculated overall differences between groups and tested for interactions with age, diabetes, race-ethnicity (white, black, and Hispanic), body mass index (BMI), and hormone therapy (HT).

RESULTS

The intervention women experienced significantly greater reductions in percentage body fat, FM, and LM at years 1 and 3 than did women in the comparison group (all P < 0.05). At year 6, only the FM change was significantly different between groups. Overall, the intervention was associated with reductions in percentage body fat (-0.8%; 95% CI: -1.0%, -0.6%), FM (-1.1 kg; 95% CI: -1.3, -0.8 kg), and LM (-0.17 kg; 95% CI: -0.28, -0.06 kg) during follow-up (all P < 0.003). Intervention associations varied by race-ethnicity, BMI, diabetes, and HT and remained significant after adjustment for physical activity.

CONCLUSION

This intervention was associated with modest long-term body-composition changes; the findings were more robust in years 1 and 3. This trial was registered at clinicaltrials.gov as NCT00000611.

Adherence to a behavioral weight loss treatment program enhances weight loss and improvements in biomarkers

OBJECTIVES

To describe participants' adherence to multiple components (attendance, energy intake, fat gram, exercise goals, and self-monitoring eating and exercise behaviors) of a standard behavioral treatment program (SBT) for weight loss and how adherence to these components may influence weight loss and biomarkers (triglycerides, low density lipoproteins [LDL], high density lipoprotein, and insulin) during the intensive and less-intensive intervention phases.

METHODS

A secondary analysis of a randomized clinical trial consisting of a SBT with either fat-restricted standard or lacto-ovo vegetarian diet. The 12-month intervention was delivered in 33 group sessions. The first six months reflected the intensive phase; the second six months, the less-intensive intervention phase. We conducted the analysis without regard to treatment assignment. Eligible participants included overweight/obese adults (N = 176; mean body mass index = 34.0 kg/m(2)). The sample was 86.9% female, 70.5% White, and 44.4 +/- 8.6 years old. The outcome measures included weight and biomarkers.

RESULTS

There was a significant decline in adherence to each treatment component over time (P < 0.0001). In the first six months, adherence to attendance, self-monitoring and the energy goal were significantly associated with greater weight loss (P < 0.05). Adherence to attendance and exercise remained significantly associated with weight loss in the second six months (P < 0.05). Adherence to attendance, self-monitoring and exercise had indirect effects through weight loss on LDL, triglycerides, and insulin (P < 0.05).

CONCLUSIONS

We observed a decline in adherence to each treatment component as the intervention intensity was reduced. Adherence to multiple treatment components was associated with greater weight loss and improvements in biomarkers. Future research needs to focus on improving and maintaining adherence to all components of the treatment protocol to promote weight loss and maintenance.

The emperor's tailors: the failure of the medical weight loss paradigm and its causal role in the obesity of America

During the past century, the medical profession has developed a paradigm for the treatment of obesity, which prescribes specific exercise and dietary goals under the umbrella of 'lifestyle change'. It has three components, all of which evolved from origins that had nothing to do with weight control. First, it is individually prescriptive, that is weight loss is considered the responsibility of the individual as contrasted to a societal or group responsibility. Second, it recommends exercise aimed towards structured, or non-functional, activities with a variety of physiological endpoints. Last, dietary goals are defined by calories, exchanges, food groups and various nutritional components. Diets are usually grouped by these goals. This model is unique to America, it is not working and it has also played a causal role in the obesity it is attempting to eliminate. A new model must be developed, which contains an observationally based societal prescription and links activity with functional outcomes and diets, which are food rather than nutritionally based.

Effect of fat replacement by inulin or lupin-kernel fibre on sausage patty acceptability, post-meal perceptions of satiety and food intake in men

The present study examined whether replacing fat with inulin or lupin-kernel fibre influenced palatability, perceptions of satiety, and food intake in thirty-three healthy men (mean age 52 years, BMI 27·4kg/m2), using a within-subject design. On separate occasions, after fasting overnight, the participants consumed a breakfast consisting primarily of either a full-fat sausage patty (FFP) or a reduced-fat patty containing inulin (INP) or lupin-kernel fibre (LKP). Breakfast variants were alike in mass, protein and carbohydrate content; however the INP and LKP breakfasts were 36 and 37% lower in fat and 15 and 17% lower in energy density respectively compared with the FFP breakfast. The participants rated their satiety before breakfast then evaluated patty acceptability. Satiety was rated immediately after consuming the breakfast, then over the subsequent 4·5h whilst fasting. Food consumed until the end of the following day was recorded. All patties were rated above ‘neither acceptable or unacceptable’, however the INP rated lower for general acceptability (P=0·039) and the LKP lower for flavour (P=0·023) than the FFP. The LKP breakfast rated more satiating than the INP (P=0·010) and FFP (P=0·016) breakfasts. Total fat intake was 18g lower on the day of the INP (P=0·035) and 26g lower on the day of the LKP breakfast (P=0·013) than the FFP breakfast day. Energy intake was lower (1521kJ) only on the day of the INP breakfast (P=0·039). Both inulin and lupin-kernel fibre appear to have potential as fat replacers in meat products and for reducing fat and energy intake in men.

Evidence of anti-obesity effects of the pomegranate leaf extract in high-fat diet induced obese mice

OBJECTIVE

To investigate the anti-obesity effects of the pomegranate leaf extract (PLE) in a mouse model of high-fat diet induced obesity and hyperlipidemia.

DESIGN

For the anti-obesity experiment, male and female ICR mice were fed with a high-fat diet to induce obesity. When the weight of the high-fat diet group was 20% higher than the normal diet group, the animals were treated with 400 or 800 mg/kg/day of PLE for 5 weeks. Body weight and daily food intake were measured regularly during the experimental period. The various adipose pads were weighed and serum total cholesterol (TC), triglyceride (TG), glucose and high-density lipoprotein cholesterol (HDL-C) were measured after 5 weeks, treatment with PLE. In the fat absorption experiment, both the normal and obese mice were given 0.5 ml lipid emulsion and PLE at a dose of 800 mg/kg at the same time. Serial serum TG levels were measured at times 1, 2, 3, 4 and 6 h after the treatment. TGs in fecal excretions were measured after the mice were orally given a lipid emulsion. Effects of PLE and its isolated compounds (ellagic acid and tannic acid) on pancreatic lipase activity were examined in vitro.

RESULTS

The PLE-treated groups showed a significant decrease in body weight, energy intake and various adipose pad weight percents and serum, TC, TG, glucose levels and TC/HDL-C ratio after 5 weeks treatment. Furthermore, PLE significantly attenuated the raising of the serum TG level and inhibited the intestinal fat absorption in mice given a fat emulsion orally. PLE showed a significant difference in decreasing the appetite of obese mice fed a high-fat diet, but showed no effect in mice fed a normal diet.

CONCLUSION

PLE can inhibit the development of obesity and hyperlipidemia in high-fat diet induced obese mice. The effects appear to be partly mediated by inhibiting the pancreatic lipase activity and suppressing energy intake. PLE may be a novel appetite suppressant that only affects obesity owing to a high-fat diet.

Effects of two energy-restricted diets containing different fruit amounts on body weight loss and macronutrient oxidation

The consumption of specific foods in energy-restricted diets may affect the weight loss process. The purpose of this research was to evaluate whether obese women following two hypocaloric diets with distinct fruit content differ in weight loss and metabolic responses. Fifteen obese women were included, who were randomly assigned to follow a low or a high-fruit energy-restricted diet for 8 weeks. The main outcome variables were weight and fat losses. Metabolic measurements concerning macronutrient oxidation were also assessed by using (13)C labelled fructose and indirect calorimetry. The induced weight loss was similar for both diets (6.9 +/- 2% vs. 6.6 +/- 2%, p = 0.785). Both experimental diets similarly improved the lipid plasma profile in the participants, but the cholesterol fall was higher in obese subjects receiving the diet containing more fruit. No statistical differences in lipids carbohydrates and (13)C labelled fructose utilisation were observed, but protein oxidation was differently affected by the experimental diets. The compensatory effects of the associated fibre/fructose intake may explain the lack of a specific effect of the fruit amount on hypocaloric diets designed to weight loss, although the increased fibre content from enriched fruit diets may be involved in the favourable effects on cholesterol plasma levels.

In pursuit of neural risk factors for weight gain in humans

Obesity is a multifactorial disease associated with an increased risk of type 2 diabetes, coronary artery disease, cancer, and consequently, with a reduced length of life. Metabolic phenotypes of reduced energy expenditure have been associated with weight gain, but their contribution has been estimated to be relatively small. On the other hand, excessive food intake is likely to be the major determinant of positive energy balances and it is underlied by both non-conscious (homeostatic) and conscious (perceptual, emotional, and cognitive) phenomena processed in the brain. Functional neuroimaging is a promising tool to investigate these neural substrates in humans, because it provides a measurement of state-dependent brain regional activity, bridging the gap between neural events and behavioral responses. Using this technology, a few studies have provided the first evidence of functional differences between obese and lean individuals in the brain's response to energy intake and investigated the presence of neural risk factors of weight gain.

Dietary fat and obesity: a review of animal, clinical and epidemiological studies

The First Law of Thermodynamics provides a framework for understanding the imbalance between energy intake and expenditure that produces obesity, but it does not help understand the role of genetics, the regulation of food intake, the distribution of body fat, the mechanisms by which diets work or the mechanism by which portion control has gotten out of control. In animals, increasing dietary fat increases body fat, and it is unlikely that humans escape this important biological rule. In epidemiological studies, increasing dietary fat is associated with increased prevalence of obesity probably by increasing the intake of energy dense foods. In the National Weight Loss Registry, three things were associated with weight loss: continued monitoring of food intake, lowering dietary fat intake, and increased exercise. The relation of dietary fat is most evident when physical activity is low. The speed of adaptation to dietary fat is increased by exercise. When dietary fat is reduced, weight is lost, but weight loss eventually plateaus. The rate of weight loss during the initial phase is about 1.6 g/day for each 1% decrease in fat intake. When dietary fat is replaced with olestra to reduce fat intake from 33% to 25% in obese men, weight loss continues for about 9 months reaching a maximum of nearly 6% of body weight and a loss of 18% of initial body fat. In the control group with a 25% reduced-fat diet, weight loss stopped after 3 months and was regained over the next 6 months, indicating the difficulty of adhering to a conventional low-fat diet. Thus, dietary fat is an important contributor to obesity in some people.

Amino acid composition of soybean protein increased postprandial carbohydrate oxidation in diabetic mice

The effects of an amino acid mixture simulating dietary soybean protein on the postprandial energy metabolism was investigated using type II diabetic mice. KK-A(y) strain mice were fed restrictive isoenergetic and isonitrogenous diets (35% of energy as protein and 5% as fat) based on either casein, soybean protein isolate hydrolysate (SPI-H), SPI-HET (ethanol unsoluble fraction of SPI-H), SPI-AA and casein-AA (amino acid mixtures simulating SPI-H and casein). To measure dietary carbohydrate oxidation, the animals were fed a diet containing (13)C-glucose. Postprandial respiratory quotient and expired (13)CO(2) were higher in the SPI-AA than in the casein-AA group, as the differences were similarly observed in mice fed SPI-H and casein diet. No significant differences were observed in the postprandial respiratory quotient and expired (13)CO(2) between the SPI-H and SPI-HET group. In conclusion, this study on food-restricted mice indicates that the amino acid mixtures simulating SPI-H or casein could affect postprandial energy metabolism in diabetic mice, as observed in those fed SPI-H or casein in the form of peptide or protein.

Medical management of obesity

BACKGROUND

Obesity is associated with elevated morbidity and death rates. The World Health Organization defines obesity as a chronic disease. The percentage of obese persons is increasing worldwide. Many different treatment modalities are available. Long-term success rates are not convincing.

RESEARCH FOCUS

Overweight and obesity should be treated in an interdisciplinary and multimodal approach. The best results in loosing body weight, especially body fat use very low calorie diets followed by a fat-reduced, carbohydrate-rich diets. Weight-loss drugs should be used only in a weight-loss program including diet and physical activity. Surgical intervention is necessary in a small group of persons refractory to conservative obesity treatment.

CONCLUSIONS

New structured guidelines oriented and quality controlled programs for treatment of obese patients are necessary.

The effect of breakfast type on total daily energy intake and body mass index: results from the Third National Health and Nutrition Examination Survey (NHANES III)

OBJECTIVE

The objective of this study was to investigate the relationship between breakfast type, energy intake and body mass index (BMI). We hypothesized not only that breakfast consumption itself is associated with BMI, but that the type of food eaten at breakfast also affects BMI.

METHODS

Data from the Third National Health and Nutrition Examination Survey (NHANES III), a large, population-based study conducted in the United States from 1988 to 1994, were analyzed for breakfast type, total daily energy intake, and BMI. The analyzed breakfast categories were "Skippers," "Meat/eggs," "Ready-to-eat cereal (RTEC)," "Cooked cereal," "Breads," "Quick Breads," "Fruits/vegetables," "Dairy," "Fats/sweets," and "Beverages." Analysis of covariance was used to estimate adjusted mean body mass index (BMI) and energy intake (kcal) as dependent variables. Covariates included age, gender, race, smoking, alcohol intake, physical activity and poverty index ratio.

RESULTS

Subjects who ate RTEC, Cooked cereal, or Quick Breads for breakfast had significantly lower BMI compared to Skippers and Meat and Egg eaters (p < or = 0.01). Breakfast skippers and fruit/vegetable eaters had the lowest daily energy intake. The Meat and Eggs eaters had the highest daily energy intake and one of the highest BMIs.

CONCLUSIONS

This analysis provides evidence that skipping breakfast is not an effective way to manage weight. Eating cereal (ready-to-eat or cooked cereal) or quick breads for breakfast is associated with significantly lower body mass index compared to skipping breakfast or eating meats and/or eggs for breakfast.

Whole-body fat oxidation rate and plasma triacylglycerol concentrations in men consuming an ad libitum high-carbohydrate or low-carbohydrate diet

BACKGROUND

High-carbohydrate diets may increase plasma triacylglycerol concentrations either by increasing production of triacylglycerols or by reducing their clearance.

OBJECTIVE

We assessed whether the changes in plasma triacylglycerol concentrations induced by dietary interventions were associated with the changes in whole-body fat oxidation rates.

DESIGN

In a parallel study, 37 healthy male subjects [body mass index (in kg/m(2)): 28 +/- 5, age: 34 +/- 11 y (x +/- SD)] consumed an ad libitum high-carbohydrate (60% of energy; n = 19) or low-carbohydrate (46% of energy), high-fat (41% of energy, 23% as monounsaturated fatty acids; n = 18) diet for 7 wk. The following variables were measured before and after the dietary interventions: 1) plasma triacylglycerols before and 2, 4, 6, and 8 h after a meal (containing 40% of daily energy needs and 41% fat); 2) indirect calorimetry throughout the 8-h test; and 3) postheparin plasma lipoprotein lipase (phLPL) activity at time 8 h of the test.

RESULTS

The diets induced changes in 1) body weight: -2.5 +/- 2.8 kg (P < 0.01) and -1.7 +/- 3.1 kg (P < 0.05) and 2) fasting plasma triacylglycerols: 0.0 +/- 0.4 mmol/L (NS) and -0.3 +/- 0.3 mmol/L (P < 0.05) for the high-carbohydrate and the low-carbohydrate diets, respectively. In normoinsulinemic subjects (fasting insulin < 100 pmol/L), dietary changes in postprandial triacylglycerols were significantly predicted by changes in phLPL, body weight, respiratory quotient (or fat oxidation), and the type of diet (stepwise multiple linear regression).

CONCLUSION

Postprandial plasma triacylglycerol concentrations may depend at least partly on fat oxidation, body weight, and LPL activity.

A soybean peptide isolate diet promotes postprandial carbohydrate oxidation and energy expenditure in type II diabetic mice

The aim of the present study was to determine the effects of dietary proteins on the oxidation of dietary carbohydrate and lipids in type II diabetic mice. KK-A(y) strain mice were provided free access to a high fat diet (30% of energy as fat) for an initial 4-wk period to induce diabetes. To reduce body weight gain, the mice were subsequently fed restrictive isoenergetic and isonitrogenous diets (35% of energy as protein and 5% as fat) based on either casein or soy protein isolate hydrolysate (SPI-H) for 4 wk. To measure exogenous carbohydrate and lipid oxidation, the mice were fed a diet containing (13)C-glucose or (13)C-triolein while they were in a respiratory chamber for 72 h. Postprandial energy expenditure was higher in the SPI-H than in the casein group; this difference was due to an increase in postprandial exogenous and endogenous carbohydrate oxidation. There were no differences in 24-h energy expenditure between dietary groups. Oxidation of exogenous carbohydrate tended to be higher (P = 0.054) in the SPI-H group during the 24 h of measurement. Fecal excretion of (13)C-glucose was lower but the excretion of lipid was higher in mice fed the SPI-H diet than in casein-fed mice. These results indicate that in type II diabetic mice, dietary SPI-H not only inhibits the absorption of dietary lipids and increases the absorption of dietary carbohydrates but also augments postprandial energy expenditure, which is accompanied by a postprandial increase in oxidation of dietary carbohydrates.

Dietary fat is not a major determinant of body fat

The percentage of energy from fat in diets has been thought to be an important determinant of body fat, and several mechanisms have been proposed. Comparisons of diets and the prevalence of obesity between affluent and poor countries have been used to support this relationship, but these contrasts are seriously confounded by differences in physical activity and food availability. Within areas of similar economic development, regional intake of fat and prevalence of obesity have not been positively correlated. Randomized trials are the preferable method to evaluate the effect of dietary fat on adiposity and are feasible because the number of subjects needed is not large. In short-term trials, a modest reduction in body weight is typically seen in individuals randomized to diets with a lower percentage of calories from fat. However, compensatory mechanisms appear to operate, because in randomized trials lasting >or=1 year, fat consumption within the range of 18% to 40% of energy appears to have little if any effect on body fatness. The weighted mean difference was -0.25 kg overall and +1.8 kg (i.e., less weight loss on the low-fat diets) for trials with a control group that received a comparable intensity intervention. Moreover, within the United States, a substantial decline in the percentage of energy from fat during the last 2 decades has corresponded with a massive increase in the prevalence of obesity. Diets high in fat do not appear to be the primary cause of the high prevalence of excess body fat in our society, and reductions in fat will not be a solution.

A low-fat intake and greater activity level are associated with lower weight regain 3 years after completing a very-low-calorie diet

OBJECTIVE

To examine the roles of diet, exercise, and lifestyle factors in determining long-term weight regain after weight loss with a very-low-calorie diet (VLCD).

SUBJECTS

Twenty-seven of 38 women who lost weight with a VLCD.

DESIGN

Graduates of a weight loss intervention study returned for follow-up 3 years after program completion. Percentage of initial weight loss that was regained was correlated with subjects' fat intake (assessed via 7-day food records and a Diet Habit Survey), energy intake (assessed via 7-day food records), activity level and lifestyle factors (assessed via questionnaires) that are supportive of weight loss maintenance.

STATISTICAL ANALYSES PERFORMED

Regression analysis was used to assess the relationship of weight regain with fat intake, activity level, and energy intake. Contingency table analysis was used to assess the association between weight regain and lifestyle factors.

RESULTS

Subjects followed experienced a -20.7kg+/-9.2kg (-19.2%+/-7%) (mean+/-standard deviation) weight change during the original VLCD program and a 13.9kg+/-11.3kg (76.6%+/-52.1%) weight change 3 years post-VLCD. Fat intake, assessed by a 7-day food diary, was positively correlated with weight regain at 3 years (r=0.66, P=.0004). Less weight regain was also seen with a lower percent fat intake as reflected by a higher Diet Habit Survey score (r=-0.55, P=.004). Women with the lowest tertile of reported fat intake (<25% of energy) from the Diet Habit Survey regained the least amount of weight (P=.05). Activity level was negatively correlated with weight regain (r=-0.53, P=.005). After correction for multiple comparisons, there was no association between total energy intake and weight regain. Lifestyle factors were also not associated with weight regain.

APPLICATIONS/CONCLUSIONS

Identifying strategies to maintain weight loss is crucial because of the negative health effects and increasing prevalence of obesity. For women who have lost weight on a VLCD, limiting dietary fat intake and maintaining physical activity are both important factors for the prevention of weight regain. To promote better weight loss outcomes, registered dietitians should help clients who have lost weight limit their fat intake to less than 30% of energy and encourage high activity levels.

Dietary fat plays a major role in obesity: no

The percentage of dietary energy from fat has been suggested to be an important determinant of body fat, and this presumed effect has been invoked to justify the general promotion of low-fat diets. Dietary fat and the prevalence of obesity are lower in poor countries than in affluent countries. However, these contrasts are seriously confounded by differences in physical activity and food availability; within areas of similar economic development, per capita intake of fat and the prevalence of obesity have not been positively correlated. Randomized trials are the preferable method for evaluating the effect of dietary fat on adiposity because they avoid problems of confounding that are difficult to control in other studies. In short-term trials, a small reduction in body weight is typically seen in individuals randomized to diets with a lower percentage of calories from fat. In a meta-analysis of these trials, it was estimated that a decrease in 10% of energy from fat would reduce weight by 16 g d-1, which would correspond to a 9-kg weight loss by 18 months. However, compensatory mechanisms appear to operate because in trials lasting one year or longer, fat consumption within the range of 18-40% of energy has consistently had little, if any, effect on body fatness. Moreover, within the United States (US), a substantial decline in the percentage of energy from fat during the last two decades has corresponded with a massive increase in obesity, and similar trends are occurring in other affluent countries. Diets high in fat do not account for the high prevalence of excess body fat in Western countries; reductions in the percentage of energy from fat will have no important benefits and could further exacerbate this problem. The emphasis on total fat reduction has been a serious distraction in efforts to control obesity and improve health in general.

Effect of low-fat and/or low-energy diets on anthropometric measures in participants of the women's diet study

OBJECTIVE

To compare the effects of low-fat, low-energy and combination low-fat/low-energy intervention on changes in six anthropometric measures in Caucasian and African-American free-living women.

METHODS

The effects of dietary counseling strategies for fat and/or energy reduction were examined on anthropometric measures in 86 pre-menopausal women, average BMI of 28 kg/m2, who participated in a 12-week intervention trial called the Women's Diet Study. The dietary goals were 15% of energy from fat and/or 25% reduction in energy intake, relative to reported baseline intake, using a 2 x 2 factorial design. Analysis of covariance models were constructed to evaluate changes in anthropometric measures over the 12 weeks of study.

RESULTS

The biggest difference by race was in women who were relatively heavier at baseline, in which case African-American women lost significantly less weight but decreased their waist:hip ratio to a significantly greater extent than Caucasian women. With regard to the effects of diet arm, weight loss varied depending on baseline weight, and in women with higher baseline weights, the combination low-fat/low-energy diet resulted in the most weight loss (6.7 kg, p < 0.05). Decreases in the other anthropometric measures at week 12 were more uniform across diet arms and did not depend on baseline values. After controlling for previous weight history and race, the decreases in BMI, percent body fat and waist circumference after 12 weeks were statistically equivalent with the low-fat, low-energy or combination low-fat/low-energy diets. The relatively greater decreases in percent body fat and waist circumference with the combination diet versus the low-fat or low-energy diets were not statistically significant.

CONCLUSION

The low-fat, low-energy and combination diets all resulted in similar and statistically significant decreases in BMI, percent body fat and waist circumference over 12 weeks of intervention. The extent of weight loss, however, varied depending on baseline weight, and the combination diet was the only intervention to result in significant weight loss for women who were heavier at baseline. This indicates that, although there may be an advantage for reducing dietary fat in initially heavier women, any of these counseling strategies could be effective for improving anthropometric predictors of health risks associated with overweight status. This is useful since flexibility in dietary choices may facilitate adherence to dietary counseling in some individuals.

Lipid, protein and carbohydrate intake in relation to body mass index

OBJECTIVE

To examine whether the same amount of energy intake has different consequences on body mass index (BMI), depending on the source of energy from specific macronutrients.

DESIGN

Cross-sectional study, in the context of the European Prospective Investigation into Cancer and nutrition (EPIC).

SETTING

Communities all over Greece.

SUBJECTS

A total of 27 862 apparently healthy volunteers, men and women, ages 25-82 y.

INTERVENTIONS

None.

METHODS

Dietary information was collected through an interviewer-administered semi-quantitative food frequency questionnaire. In the context of a cross-sectional analysis, we calculated changes of BMI per increments of energy intake from protein, carbohydrates, saturated, polyunsaturated and monounsaturated lipids and ethanol, controlling for mutual confounding and other confounders, among all participants, and after exclusion of under-reporters and/or those on a diet.

RESULTS

Protein intake was positively associated with BMI. The association was evident when nutrients were not mutually adjusted for and increased after mutual adjustment among nutrients (beta=0.80 kg/m(2) per 418.4 kJ or 100 kcal increment, 95% confidence interval 0.55-1.06 for men, and beta=1.59, 95% CI 1.30-1.88 for women), as well as after exclusion of under-reporters and/or those on a diet. The effects of other macronutrients were less substantial or consistent.

CONCLUSIONS

There is evidence indicating that protein intake is conducive to obesity. Moreover, our data suggest that neither saturated or monounsaturated lipids nor carbohydrates are likely to play a major role in increasing BMI over and beyond that indicated by their energy content.

Effect of 3 modified fats and a conventional fat on appetite, energy intake, energy expenditure, and substrate oxidation in healthy men

BACKGROUND

Different dietary fats are metabolized differently in humans and may influence energy expenditure, substrate oxidation, appetite regulation, and body weight regulation.

OBJECTIVE

We examined the short-term effects of 4 triacylglycerols (test fats) on subjective appetite, ad libitum energy intake, meal-induced thermogenesis, and postprandial substrate oxidation.

DESIGN

Eleven healthy, normal-weight men (mean age: 25.1 +/- 0.5 y) consumed 4 different test fats [conventional fat (rapeseed oil) and 3 modified fats (lipase-structured fat, chemically structured fat, and physically mixed fat)] in a randomized, double-blind, crossover design.

RESULTS

No significant differences in appetite sensations or ad libitum energy intakes were observed between the 4 test fats. Overall, the 4 fats exerted different effects on energy expenditure (meal effect: P < 0.01) and substrate oxidation (interaction between meal and time: P < 0.05). In post hoc tests, the 3 modified fats resulted in significantly higher postprandial energy expenditure and fat oxidation than did the conventional fat (P < 0.008, Bonferroni adjusted); no significant differences were observed between the 3 modified fats.

CONCLUSIONS

Structured fats do not change short-term postprandial appetite sensations or ad libitum energy intakes but do result in higher postprandial energy expenditure and fat oxidation than do conventional fats and hence promote negative energy and fat balance. In humans, a physically mixed fat (trioctanoate + rapeseed oil) is metabolized as quickly as are structured fats. The position of medium-chain fatty acids on the glycerol backbone of triacylglycerols does not seem to affect energy expenditure or appetite.

A review of current weight management: research and recommendations

PURPOSE

To review current research and recommendations on weight loss and weight control and provide suggestions for health care providers who furnish weight management counseling.

DATA SOURCES

Scientific publications, clinical guidelines, and government sources.

CONCLUSIONS

Research reaffirms the long-held understanding that weight loss can be accomplished only through a reduction in the number of calories consumed and an increase in exercise. Weight maintenance requires life-long behavioral change combining moderate exercise, lower fat intake, increased fruit and vegetable consumption, as well as social support. Fad diets and medications are not the answer to long-term weight maintenance.

IMPLICATIONS FOR PRACTICE

The essential components of a weight loss or weight management program include: calorie reduction of 300-500 calories per day, appropriate exercise, variety in food choices, increased consumption of grains, fruits, and vegetables, and reduction of fat to no more than 30% of daily calories. Clients should be referred to dietitian and exercise consultants as needed.

The role of low-fat diets in body weight control: a meta-analysis of ad libitum dietary intervention studies

OBJECTIVES

Low-fat high-carbohydrate diets are recommended to prevent weight gain in normal weight subjects and reduce body weight in overweight and obese. However, their efficacy is controversial. We evaluated the efficacy of ad libitum low-fat diets in reducing body weight in non-diabetic individuals from the results of intervention trials.

DESIGN

Studies were identified from a computerized search of the Medline database from January 1966 to July 1999 and other sources. Inclusion criteria were: controlled trials lasting more than 2 months comparing ad libitum low-fat diets as the sole intervention with a control group consuming habitual diet or a medium-fat diet ad libitum.

MAIN OUTCOME MEASURES

Differences in changes in dietary fat intake, energy intake and body weight. Weighted mean differences for continuous data and 95% confidence intervals (CIs) were calculated.

RESULTS

Two authors independently selected the studies meeting the inclusion criteria and extracted data from 16 trials (duration of 2-12 months) with 19 intervention groups, enrolling 1910 individuals. Fourteen were randomized. Weight loss was not the primary aim in 11 studies. Before the interventions the mean proportions of dietary energy from fat in the studies were 37.7% (95% CI, 36.9-38.5) in the low-fat groups, and 37.4% (36.4-38.4) in the control groups. The low-fat intervention produced a mean fat reduction of 10.2% (8.1-12.3). Low-fat intervention groups showed a greater weight loss than control groups (3.2 kg, 95% confidence interval 1.9-4.5 kg; P < 0.0001), and a greater reduction in energy intake (1 138 kJ/day, 95% confidence interval 564-1712 kJ/day, P = 0.002). Having a body weight 10 kg higher than the average pre-treatment body weight was associated with a 2.6 +/- 0.8 kg (P = 0.011) greater difference in weight loss.

CONCLUSION

A reduction in dietary fat without intentional restriction of energy intake causes weight loss, which is more substantial in heavier subjects.

Effect of fat-reduced diets on 24-h energy expenditure: comparisons between animal protein, vegetable protein, and carbohydrate

BACKGROUND

Single-meal tests have shown that protein has greater thermogenic and satiating effects than does carbohydrate, which may be relevant for the prevention and treatment of obesity if these effects can be maintained over 24 h.

OBJECTIVE

The effects of pork-meat protein, soy protein, and carbohydrate on 24-h energy expenditure were compared.

DESIGN

Twelve young, healthy, overweight and mildly obese [body mass index (in kg/m(2)): 26-32] nonsmoking men participated in a randomized, single-blind, 3-way crossover study lasting 4 d. The intervention had a 1-10-wk washout period. The 3 isoenergetic intervention diets were as follows: pork diet (29% of energy as fat and 29% as protein, mainly from pork meat), soy diet (29% of energy as fat and 28% as protein, mainly from soy), and carbohydrate diet (28% of energy as fat and 11% as protein). Twenty-four-hour energy expenditure was measured in a respiratory chamber at baseline and on day 4 of each intervention period.

RESULTS

Twenty-four-hour energy expenditure was higher with the pork than with the soy (248 kJ/d, 1.9%; P: = 0.05) or carbohydrate (492 kJ/d, 3.9%; P: < 0.0001) diet and higher with the soy than with the carbohydrate (244 kJ/d, 1.9%; P: < 0.05) diet. However, because of a higher satiating effect, energy intake was 10-15% lower during the chamber stay than at baseline (P: > 0.05) with all 3 diets. The differences in energy expenditure remained unchanged after adjustment for differences in 24-h energy balance.

CONCLUSIONS

Substitution of carbohydrate with 17-18% of energy as either pork-meat or soy protein produced a 3% higher 24-h energy expenditure. The animal protein in pork meat produced a 2% higher 24-h energy expenditure than did the vegetable protein in soy.

Types of fat intake and body mass index in a Mediterranean country

BACKGROUND

Although the fatty acid fractions provide similar metabolizable energy, the type of dietary fat consumed could be relevant to the development of obesity.

OBJECTIVE

To investigate the relationship between body mass index (BMI), obesity and the consumption of different types of fat and olive oil in a Mediterranean country with high prevalence of obesity, and high intake of monounsaturated fatty acids (MUFA) and olive oil.

SUBJECTS

The study was carried out in Spain among 23 289 women and 14 374 men, aged 29-69 years, who were participants of a large European prospective cohort.

METHODS

: Information on usual food intake was collected by interviewers by means of a dietary history questionnaire. The association between obesity (BMI >/= 30 kg m2), dietary fat, other dietary patterns and other non-dietary factors were tested using multilinear regression analysis. The ratio of reported energy intake to energy requirement was used as an estimation of dietary underreporting.

RESULTS

The association between fatty acid fractions intake (saturated fatty acids (SFA) in women, and MUFA and polyunsaturated fatty acids (PUFA) in both sexes) and BMI was very weak, accounting for less than 1% of variance. All dietary and non-dietary variables accounted for 21% of variance in the measurement of BMI in women and only 6.7% of variance in men. Estimated underreporting of energy intake was 17.5% in obese women and 5.5% in obese men.

CONCLUSIONS

The association between consumption of specific types of dietary fat, olive oil and obesity in Spain is not very important. However, because of the cross-sectional design and some level of underreporting of energy intake observed in overweight subjects and overreporting in underweight subjects, systematic bias cannot be completely discarded.

The sympathetic nervous system and obesity: role in aetiology and treatment

The sympathetic nervous system (SNS) is an important component of the autonomic nervous system, and thus plays a major role in the maintenance of homeostasis. The SNS is of particular importance in the control of the cardiovascular system and of a number of metabolic processes. Alterations in SNS effects on metabolism have been implicated in the development and maintenance of obesity, and the SNS is a potential therapeutic target in the treatment of obesity. This review provides an overview of the anatomical and physiological aspects of the SNS, before considering the evidence showing a role for the SNS in the development or treatment of obesity.

The role of dietary fat in body fatness: evidence from a preliminary meta-analysis of ad libitum low-fat dietary intervention studies

The role of high-fat diets in weight gain and obesity has been questioned because of inconsistent reports in the literature concerning the efficacy of ad libitum low-fat diets to reduce body weight. We conducted a meta-analysis of weight loss occurring on ad libitum low-fat diets in intervention trials, and analysed the relationship between initial body weight and weight loss. We selected controlled trials lasting more than 2 months comparing ad libitum low-fat diets with a control group consuming their habitual diet or a medium-fat diet ad libitum published from 1966 to 1998. Data were included from 16 trials with a duration of 2-12 months, involving 1728 individuals. No trials on obese subjects fulfilled the inclusion criteria. The weighted difference in weight loss between intervention and control groups was 2.55 kg (95% CI, 1.5-3.5; P < 0.0001). Weight loss was positively and independently related to pre-treatment body weight (r = 0.52, P < 0.05) and to reduction in the percentage of energy as fat (0.37 kg/%, P < 0.005) in unweighted analysis. Extrapolated to a BMI of about 30 kg/m2 and assuming a 10% reduction in dietary fat, the predicted weight loss would be 4.4 kg (95% CI, 2.0 to -6.8 kg). Because weight loss was not the primary aim in 12 of the 16 studies, it is unlikely that voluntary energy restriction contributed to the weight loss. Although there is no evidence that a high intake of simple sugars contributes to passive overconsumption, carbohydrate foods with a low glycaemic index may be more satiating and exert more beneficial effects on insulin resistance and cardiovascular risk factors. Moreover, an increase in protein content up to 25% of total energy may also contribute to reducing total energy intake. In conclusion, a low-fat diet, high in protein and fibre-rich carbohydrates, mainly from different vegetables, fruits and whole grains, is highly satiating for fewer calories than fatty foods. This diet composition provides good sources of vitamins, minerals, trace elements and fibre, and may have the most beneficial effect on blood lipids and blood-pressure levels. A reduction in dietary fat without restriction of total energy intake prevents weight gain in subjects of normal weight and produces a weight loss in overweight subjects, which is highly relevant for public health.

Effects of reduced-fat diets consumed ad libitum on intake of nutrients, particularly antioxidant vitamins

OBJECTIVES

To determine whether a reduced-fat diet consumed ad libitum can achieve the recommended intakes of other macronutrients, fiber, and cholesterol and whether such a diet affects intake of other important micronutrients such as fat-soluble vitamins.

DESIGN

Twelve-month, randomized, controlled trial of a reduced-fat, ad libitum diet vs usual diet.

SUBJECTS

One hundred ten adults older than 40 years with glucose intolerance (2-hour blood glucose concentration = 7.0 to 11.0 mmol/L) who were selected from a previous workforce survey.

INTERVENTION

Monthly small-group meetings aimed at identifying sources of dietary fat and ways to reduce fat consumption.

MAIN OUTCOME MEASURES

Nutrient intakes derived from 3-day food diaries at the beginning and end of the study. Blood levels of retinol, alpha-tocopherol, and beta carotene at the end of the study.

STATISTICAL ANALYSES PERFORMED

Unpaired t tests for determining changes in nutrient intake and antioxidant vitamin concentrations. Separate analyses were conducted with users of mineral and vitamin supplements and people who changed smoking status to reduce potential confounding.

RESULTS

Fat intake decreased from 35% to 26% of energy in the reduced-fat diet group compared with a 2% decrease in the control group (P < .0001). Total energy intake also decreased in the 2 groups (-362 vs -59 kcal/day, P < .02). Those changes were reflected in a 3.1 +/- 4.7 kg (mean +/- standard deviation) weight loss in the intervention group compared with a 0.4 +/- 3.0 kg weight gain in the control group (P < .0001). There were no differences between groups in the changes in micronutrient intakes, except for an energy-adjusted increase in beta carotene intake in the reduced-fat diet group. Serum retinol and alpha-tocopherol concentrations were not different between the groups, but the reduced-fat diet group had higher beta carotene concentrations (P = .009).

APPLICATIONS

A reduced-fat, ad libitum diet can be prescribed to improve overall macronutrient intake and achieve modest weight loss without sacrificing micronutrient intakes.

Macronutrient balances and obesity: the role of diet and physical activity

Observational cross-sectional and longitudinal studies suggest that a high fat diet and physical inactivity are independent risk factors for weight gain and obesity. Mechanistic and intervention studies support that fat possesses a lower satiating power than carbohydrate and protein, and a diet low in fat therefore decreases energy intake. The effect of dietary fat on energy balance is enhanced in susceptible subjects, particularly in sedentary individuals with a genetic predisposition to obesity who consume a high fat diet. Dietary carbohydrate promotes its own oxidation by an insulin-mediated stimulation of glucose oxidation. In contrast, high fat meals do not increase fat oxidation acutely. A sedentary life-style and low physical fitness cause a low muscular fat oxidation -capacity, and the consumption of a high fat diet by these individuals promotes fat storage in a synergistic fashion. Ad libitum low fat diets cause weight loss proportional to pre-treatment body weight in a dose-dependent way, i.e. weight loss is correlated positively to the reduction in dietary fat content. Increased physical activity prevents relapse after weight loss and studies have shown that those who keep up a higher level of physical activity are more successful in maintaining the reduced body weight. In conclusion, important interactions exist between genetic make up, dietary fat and physical fitness, so that a low fitness level and susceptible genes reduce muscular fat oxidation capacity which may decrease the tolerance of dietary fat. Increasing daily physical activity and reducing dietary fat content may be more effective when combined than when separate in preventing weight gain and obesity.

New understanding in obesity research

A public-health approach considers the relevance of nutritional research in the prevention and management of obesity. Well-defined and internationally-agreed definitions based on BMI allow an assessment of the worldwide prevalence of overweight and obesity. There are about 250 million obese adults in the world, and many more overweight. Obesity is emerging in the Third World, first in urban middle-aged women. With economic developments, obesity then occurs in men and younger women. In the West childhood obesity is rapidly emerging, with concern that early-onset obesity is especially hazardous. In Asians the risks of excess visceral fat occur at lower body weights than in Caucasians. The propensity to visceral obesity in Asians may relate to malnourished mothers and low birth weight. The International Obesity Task Force is considering many issues, including the health economics of obesity. It has developed a strategy to define childhood obesity, which in children over 6 years is likely to predict long-term weight and health problems. While the search for genetic markers of obesity continues, with particular interest in the leptin gene, it is clear that societal change, with the decline in physical activity and the passive overconsumption of high-fat diets are major contributors to the global increase in obesity. The public-health aspects of obesity research are therefore challenging.

The Nutrition Society Medical Lecture. Obesity: from molecules to man

Obesity is now a major public health problem in both developed and developing countries. In the UK over 16% men and 17.5% women are obese, an increase of more than 100% since 1980. However, interventions to prevent and treat obesity are hampered by an inadequate understanding of the aetiology of this condition. The present paper considers the current state of knowledge regarding the causes of obesity, including some of the genetic, metabolic, behavioural and environmental factors which influence energy balance. The present paper comprises The Nutrition Society Medal Lecture and focuses in particular on the research carried out at the MRC Dunn Nutrition Centre in Cambridge. It argues that despite decades of intensive research there is relatively little evidence of genetic or metabolic defects to explain the majority of cases of human obesity. Instead we must look to behavioural and/or environmental factors which may be underpinning the current epidemic of obesity.

The American paradox: the role of energy-dense fat-reduced food in the increasing prevalence of obesity

Although surveys have reported that the fat content of the diet has decreased over past decades, the prevalence of obesity has continued to rise in Europe and North America. This phenomenon, 'the American paradox', has been attributed partly to an inability of the reduction in dietary fat to reduce excess body fat, and partly to the over-consumption of low-fat products, which, despite their reduced fat content, have in some cases been accused of maintaining a high energy density due to low fibre and water contents, and a high content of refined carbohydrates. In Denmark, the prevalence of obesity has increased in a period in which national dietary surveys have reported a reduction of more than 10% in dietary fat content. Analysing the Danish situation, it seems unlikely that the occurrence of the American paradox in Denmark is caused by the increased consumption of energy-dense, low-fat foods. Other explanations, e.g. the under-reporting of dietary fat in surveys and the clustering of obesity-promoting lifestyles in subgroups of the population, should be sought.

The role of reduced fat diets and fat substitutes in the regulation of energy and fat intake and body weight

The suggested link between a high intake of dietary fat and obesity has led to a proliferation on the market of reduced fat foods. The preceding year has seen the publication of more long-term studies investigating the effects of reduced fat and fat substituted foods on energy intake, fat intake and body weight. Effects on the proportion of the diet consumed as fat are encouraging (with most studies showing a decrease towards dietary recommendations), whilst effects on energy intake and body weight remain equivocal.