Long-term effects of 2 energy-restricted diets differing in glycemic load on dietary adherence, body composition, and metabolism in CALERIE: a 1-y randomized controlled trial

Effect of caloric restriction in non-obese humans on physiological, psychological and behavioral outcomes

The focus of this review is on current research involving long-term calorie restriction (CR) and the resulting changes observed in physiological and behavioral outcomes in humans. Special emphasis will be given to the first completed clinical studies which are currently investigating the effects of controlled, high-quality energy-restricted diets on both biomarkers of longevity and on the development of chronic diseases related to age in humans. Prolonged CR has been shown to extend both the median and maximal lifespans in a variety of lower species such as yeast, worms, fish, rats, and mice. Mechanisms of this CR-mediated lifespan extension are not fully elucidated, but possibly involve significant alterations in energy metabolism, oxidative damage, insulin sensitivity, and functional changes in both the neuroendocrine and sympathetic nervous systems. In this brief report, we review some of the major physiological, psychological and behavioral changes after 6 months of CR in overweight otherwise healthy volunteers. Ongoing studies of prolonged CR in humans are now making it possible to analyze changes in "biomarkers of longevity" to unravel some of the mechanisms of its anti-aging phenomenon. With the incremental expansion of research endeavors in the area of energy or calorie restriction, data on the effects of CR in animal models and human subjects are becoming more accessible. Detailed analyses from controlled human trials involving long-term CR will allow investigators to link observed alterations from body composition down to changes in molecular pathways and gene expression, with their possible effects on the biomarkers of aging.

Mechanisms underlying caloric restriction and lifespan regulation: implications for vascular aging

This review focuses on the emerging evidence that attenuation of the production of reactive oxygen species and inhibition of inflammatory pathways play a central role in the antiaging cardiovascular effects of caloric restriction. Particular emphasis is placed on the potential role of the plasma membrane redox system in caloric restriction-induced pathways responsible for sensing oxidative stress and increasing cellular oxidative stress resistance. We propose that caloric restriction increases bioavailability of NO, decreases vascular reactive oxygen species generation, activates the Nrf2/antioxidant response element pathway, inducing reactive oxygen species detoxification systems, exerts antiinflammatory effects, and, thereby, suppresses initiation/progression of vascular disease that accompany aging.

Low-carbohydrate, high-protein diets revisited

PURPOSE OF REVIEW

There has been continued interest in the physiological, nutritional and clinical aspects of low-carbohydrate diets. This review will discuss the effects on appetite regulation, metabolic parameters, body weight and body composition, the role of glycemic index and glycemic load, as well as long-term outcomes.

RECENT FINDINGS

Low-carbohydrate, high-protein diets appear to improve satiety through their actions on measures of adiposity and gut peptides that influence appetite and caloric intake. Specific macronutrients such as low glycemic index carbohydrates and dietary protein impact appetite, calorie intake and metabolic parameters independent of weight loss. Long-term data, however, continue to support that total weight loss among low-carbohydrate dieters is not significantly different from low-fat dieters. The long-term safety of low-carbohydrate, high-protein diets on cardiovascular disease risk remains undetermined.

SUMMARY

Low-carbohydrate, high-protein diets may be an effective choice for weight loss, enhanced satiety and improved metabolic parameters.

Nutrition transition and its relationship to the development of obesity and related chronic diseases

The prevalence of overweight and obesity has also increased substantially in the nutritional transition countries, and the health burden of obesity-related complications is growing. The introduction of fast-food chains and Westernized dietary habits providing meals with fast-food characteristics seems to be a marker of the increasing prevalence of obesity. The mechanisms involved are probably that the supply of foods is characterized by large portion sizes with a high energy density, and sugar-rich soft drinks. The high energy density of foods is partly brought about by a high dietary fat content, and it has been shown that even in a Chinese population the increase from about 15% to 20% in the proportion of calories from fat is sufficient to explain some weight gain in the population. In addition, fast food from major chains in most countries still contains unacceptably high levels of industrially produced trans fatty acids that have powerful biological effects, and contribute to type 2 diabetes and coronary artery disease. New evidence also suggests that a high intake of trans fat may produce abdominal obesity, an important factor in the metabolic syndrome, type 2 diabetes and cardiovascular disease. The optimal diet for the prevention of weight gain, obesity, metabolic syndrome and type 2 diabetes is fat-reduced, without any industrially produced trans fatty acids, fibre-rich, high in low energy density carbohydrates (fruit, vegetables and whole grain products) and with a restricted intake of energy-containing drinks.

Carbohydrate intake and obesity

The prevalence of obesity has increased rapidly worldwide and the importance of considering the role of diet in the prevention and treatment of obesity is widely acknowledged. This paper reviews data on the effects of dietary carbohydrates on body fatness. Does the composition of the diet as related to carbohydrates affect the likelihood of passive over-consumption and long-term weight change? In addition, methodological limitations of both observational and experimental studies of dietary composition and body weight are discussed. Carbohydrates are among the macronutrients that provide energy and can thus contribute to excess energy intake and subsequent weight gain. There is no clear evidence that altering the proportion of total carbohydrate in the diet is an important determinant of energy intake. However, there is evidence that sugar-sweetened beverages do not induce satiety to the same extent as solid forms of carbohydrate, and that increases in sugar-sweetened soft drink consumption are associated with weight gain. Findings from studies on the effect of the dietary glycemic index on body weight have not been consistent. Dietary fiber is associated with a lesser degree of weight gain in observational studies. Although it is difficult to establish with certainty that fiber rather than other dietary attributes are responsible, whole-grain cereals, vegetables, legumes and fruits seem to be the most appropriate sources of dietary carbohydrate.

A novel interaction between dietary composition and insulin secretion: effects on weight gain in the Quebec Family Study

BACKGROUND

Clinical trials of low-fat diets characteristically produce small mean long-term weight loss but a large interindividual variation in response. This variation has been attributed to psychological and behavioral factors, although biological differences may also play a role.

OBJECTIVE

The objective was to determine whether physiologic differences in insulin secretion explain differences in weight gain among individuals consuming low- and high-fat diets.

DESIGN

Of 276 individuals followed in the Quebec Family Study for a mean of 6 y, we compared those in the lowest with those in the highest dietary fat tertiles. We performed oral-glucose-tolerance tests at baseline and examined the insulin concentration at 30 min (insulin-30) as a proxy measure of insulin secretion. Six-year changes in body weight and waist circumference were the primary endpoints. We determined the associations between insulin-30 and the primary endpoints by linear regression analysis, with adjustment for potentially confounding factors.

RESULTS

Mean changes in body weight and waist circumference did not differ significantly between the lowest- and highest-fat diet groups. However, these endpoints were strongly associated with insulin-30, especially among individuals consuming the lowest-fat diet. Insulin-30 at baseline was significantly associated with 6-y weight gain (r = 0.51, P < 0.0001) and change in waist circumference (r = 0.55, P < 0.0001) in the lowest diet fat, group [corrected], but not in the highest diet fat group (r = 0.18, P = 0.086 and r = 0.20, P = 0.058, respectively) [corrected] Individuals in the highest insulin-30 and lowest dietary fat group gained 1.8 kg more than did those in the highest insulin-30 and highest dietary fat group (51%; P = 0.034); they gained 4.5 kg more than did those in the lowest insulin-30 and lowest dietary fat group (6.5-fold; P = 0.0026).

CONCLUSION

A proxy measure of insulin secretion strongly predicts changes in body weight and waist circumference over 6 y in adults, especially among those consuming lower-fat diets, which demonstrates the existence of a novel diet-phenotype interaction.

Chronic calorie restriction increases susceptibility of laboratory mice (Mus musculus) to a primary intestinal parasite infection

Long-term calorie restriction (CR) has numerous benefits; however, effects of CR on susceptibility to intact pathogens are not well understood. Because CR enhances immune function of laboratory mice (Mus musculus), it was hypothesized that mice subjected to CR would be less susceptible to experimental infections of the intestinal parasite Heligmosomoides bakeri. Furthermore, because H. bakeri must combat a greater host immune response by CR mice compared to fully fed mice, it also was also hypothesized that (i) worms living in CR hosts would have lower reproduction than worms from ad libitum-fed mice, and (ii) CR mice would have a more female-biased sex ratio as male worms may be more vulnerable to host immune response than female worms. Mice were subjected to CR for 6.7 months and were then infected with H. bakeri for one additional month. As expected, CR mice had equal or enhanced immune response (eosinophils and immunoglobin G1 production) to H. bakeri infection compared to ad libitum-fed mice, and CR mice harbored a more female-biased sex ratio than ad libitum-fed mice. Contrary to predictions, CR mice had more worms than ad libitum-fed mice and the worms from CR mice produced more eggs than worms from ad libitum-fed mice. These data indicate that, despite the evidence that long-term CR enhances traditional measures of immune function, CR may actually increase susceptibility to intact parasite infection. Furthermore, changes in worm reproduction and differential survival of male vs. female worms may influence host-parasite transmission dynamics during long-term host CR.

Food cravings and energy regulation: the characteristics of craved foods and their relationship with eating behaviors and weight change during 6 months of dietary energy restriction

OBJECTIVE

To examine characteristics of craved foods in relation to dietary energy restriction (ER) with high (HG) and low glycemic load (LG) diets.

DESIGN

Assessments of food cravings before and during a randomized controlled trial of HG and LG diets provided for 6 months.

SUBJECTS

Thirty-two healthy, overweight women aged 20-42 years.

MEASUREMENTS

Self-reported food cravings and dietary intake, body weight, weight history and measures of eating behaviors.

RESULTS

Foods craved at baseline were more than twice as high in energy density as the habitual diet (3.7+/-1.5 vs 1.7+/-0.3 kcal/g; P<0.001), and on average were lower in protein (P<0.001) and fiber (P<0.001) and higher in fat (P=0.002). There were no statistically significant changes in nutritional characteristics of craved foods after 6 months of ER. There was a significant relationship between reported portion size of craved food consumed at baseline and lifetime high body mass index (r=0.49, P=0.005). Additionally, there was a significant association between susceptibility to hunger and craving frequency at baseline, and there were significant relationships between hunger score, craving frequency, strength and percentage of time that cravings are given in to after 6 months of ER. In multiple regression models, subjects who lost a greater percentage of weight craved higher energy-dense foods at month 6 of ER, but also reported giving in to food cravings less frequently (adjusted R (2)=0.31, P=0.009).

CONCLUSION

High energy density and fat content, and low protein and fiber contents were identifying characteristics of craved foods. The relationships between craving variables and hunger score suggest that the relative influence of hunger susceptibility on cravings may be important before and especially after ER. Portion size of craved foods and frequency of giving in to food cravings appear to be important areas for focus in lifestyle modification programs for long-term weight loss.