Effect of a high or a low fat diet on cardiovascular risk factors in male and female runners

Recommendations and Nutritional Considerations for Female Athletes: Health and Performance

Optimal nutrition is an important aspect of an athlete’s preparation to achieve optimal health and performance. While general concepts about micro- and macronutrients and timing of food and fluids are addressed in sports science, rarely are the specific effects of women’s physiology on energy and fluid needs highly considered in research or clinical practice. Women differ from men not only in size, but in body composition and hormonal milieu, and also differ from one another. Their monthly hormonal cycles, with fluctuations in estrogen and progesterone, have varying effects on metabolism and fluid retention. Such cycles can change from month to month, can be suppressed with exogenous hormones, and may even be manipulated to capitalize on ideal timing for performance. But before such physiology can be manipulated, its relationship with nutrition and performance must be understood. This review will address general concepts regarding substrate metabolism in women versus men, common menstrual patterns of female athletes, nutrient and hydration needs during different phases of the menstrual cycle, and health and performance issues related to menstrual cycle disruption. We will discuss up-to-date recommendations for fueling female athletes, describe areas that require further exploration, and address methodological considerations to inform future work in this important area.

Physiological and nutritional aspects of post-exercise recovery: specific recommendations for female athletes

Gender-based differences in the physiological response to exercise have been studied extensively for the last four decades, and yet the study of post-exercise, gender-specific recovery has only been developing in more recent years. This review of the literature aims to present the current state of knowledge in this field, focusing on some of the most pertinent aspects of physiological recovery in female athletes and how metabolic, thermoregulatory, or inflammation and repair processes may differ from those observed in male athletes. Scientific investigations on the effect of gender on substrate utilization during exercise have yielded conflicting results. Factors contributing to the lack of agreement between studies include differences in subject dietary or training status, exercise intensity or duration, as well as the variations in ovarian hormone concentrations between different menstrual cycle phases in female subjects, as all are known to affect substrate metabolism during sub-maximal exercise. If greater fatty acid mobilization occurs in females during prolonged exercise compared with males, the inverse is observed during the recovery phase. This could explain why, despite mobilizing lipids to a greater extent than males during exercise, females lose less fat mass than their male counterparts over the course of a physical training programme. Where nutritional strategies are concerned, no difference appears between males and females in their capacity to replenish glycogen stores; optimal timing for carbohydrate intake does not differ between genders, and athletes must consume carbohydrates as soon as possible after exercise in order to maximize glycogen store repletion. While lipid intake should be limited in the immediate post-exercise period in order to favour carbohydrate and protein intake, in the scope of the athlete's general diet, lipid intake should be maintained at an adequate level (30%). This is particularly important for females specializing in long-duration events. With protein balance, it has been shown that a negative nitrogen balance is more often observed in female athletes than in male athletes. It is therefore especially important to ensure that this remains the case during periods of caloric restriction, especially when working with female athletes showing a tendency to limit their caloric intake on a daily basis. In the post-exercise period, females display lower thermolytic capacities than males. Therefore, the use of cooling recovery methods following exercise, such as cold water immersion or the use of a cooling vest, appear particularly beneficial for female athletes. In addition, a greater decrease in arterial blood pressure is observed after exercise in females than in males. Given that the return to homeostasis after a brief intense exercise appears linked to maintaining good venous return, it is conceivable that female athletes would find a greater advantage to active recovery modes than males. This article reviews some of the major gender differences in the metabolic, inflammatory and thermoregulatory response to exercise and its subsequent recovery. Particular attention is given to the identification of which recovery strategies may be the most pertinent to the design of training programmes for athletic females, in order to optimize the physiological adaptations sought for improving performance and maintaining health.

Influence of exercise on nutritional requirements

There is no consensus on the best diet for exercise, as many variables influence it. We propose an approach that is based on the total energy expenditure of exercise and the specific macro- and micronutrients used. di Prampero quantified the impact of intensity and duration on the energy cost of exercise. This can be used to determine the total energy needs and the balance of fats and carbohydrates (CHO). There are metabolic differences between sedentary and trained persons, thus the total energy intake to prevent overfeeding of sedentary persons and underfeeding athletes is important. During submaximal sustained exercise, fat oxidation (FO) plays an important role. This role is diminished and CHO's role increases as exercise intensity increases. At super-maximal exercise intensities, anaerobic glycolysis dominates. In the case of protein and micronutrients, specific recommendations are required. We propose that for submaximal exercise, the balance of CHO and fat favors fat for longer exercise and CHO for shorter exercise, while always maintaining the minimal requirements of each (CHO: 40% and fat: 30%). A case for higher protein (above 15%) as well as creatine supplementation for resistance exercise has been proposed. One may also consider increasing bicarbonate intake for exercise that relies on anaerobic glycolysis, whereas there appears to be little support for antioxidant supplementation. Insuring minimal levels of substrate will prevent exercise intolerance, while increasing some components may increase exercise tolerance.

Preference for full-fat over low-fat foods among individuals suffering from coronary heart disease and healthy controls

Dietary behaviour can modify the risks for coronary heart disease (CHD). Dietary fat contributes to the sensory characteristics of many foods, but there are individual differences in liking for regular and reduced fat products. Preference for dietary fat might differ between healthy individuals and those of diagnosed CHD status. Preference for full-fat versus low-fat foods was assessed in a group suffering from CHD (N=24) and a healthy control group (N=41). Preferences were evaluated using a series of paired preference tests including 34 food pairs. Further, patterns across fat preference and a range of known risk factors for CHD were examined. The study was conducted in Sweden; March 2004 until May 2006. Overall the full-fat food items were preferred to the low-fat alternatives by both patients and control participants. The pattern of preference responses diverged significantly between patients and controls on only four of the 34 food items, in both directions, why preference related to total fat content per se is not confirmed as differentiating significantly between a group diagnosed with CHD compared to a healthy control group.

Effect of dietary fat on serum and intramyocellular lipids and running performance

PURPOSE

This study evaluated whether lowering IMCL stores via 3-d consumption of very-low-fat (LFAT) diet impairs endurance performance relative to a moderate-fat diet (MFAT), and whether such a diet unfavorably alters lipid profiles.

METHODS

Twenty-one male and female endurance-trained runners followed a controlled diet and training regimen for 3 d prior to consuming either a LFAT (10% fat) or MFAT (35% fat) isoenergetic diet for another 3 d in random crossover fashion. On day 7, runners followed a glycogen normalization protocol (to equalize glycogen stores) and then underwent performance testing (90-min preload run at 62 +/- 1% VO2max followed by a 10-km time trial) on the morning of day 8. Muscle biopsies obtained from vastus lateralis before and after performance testing were analyzed for IMCL (via electron microscopy) and glycogen content (via enzymatic methodology).

RESULTS

Despite approximately 30% lower IMCL (0.220 +/- 0.032% LFAT, 0.316 +/- 0.049% MFAT; P = 0.045) and approximately 22% higher muscle glycogen stores at the start of performance testing (P = 0.10), 10-km performance time was not significantly different following the two diet treatments (43.5 +/- 1.4 min LFAT vs 43.7 +/- 1.2 min MFAT). However, LFAT produced less favorable lipid profiles (P < 0.01) by increasing fasting triglycerides (baseline = 84.9 +/- 8.6; LFAT = 118.7 +/- 10.0 mg.dL(-1)) and the total cholesterol:HDL cholesterol ratio (baseline = 3.42 +/- 0.13:1; LFAT = 3.75 +/- 0.20:1), whereas MFAT lowered triglycerides (baseline = 97.5 +/- 12.2; MFAT = 70.9 +/- 7.1 mg.dL(-1)) and the total cholesterol:HDL cholesterol ratio (baseline = 3.47 +/- 0.18:1; MFAT = 3.33 +/- 0.14:1).

CONCLUSION

The results suggest that reducing IMCL via 3-d consumption of a LFAT diet does not impair running performance lasting a little over 2 h (compared with 3-d consumption of a MFAT diet plus 1-d glycogen normalization), but that even short-term consumption of a LFAT diet may unfavorably alter serum lipids, even in healthy, endurance-trained runners.

The atherogenic potential of dietary carbohydrate

OBJECTIVE

To investigate the role of dietary carbohydrate in atherogenesis.

METHOD

Search of the literature for relevant papers concerning the relationship of insulin/hyperinsulinemia and carbohydrate on the one hand, and the renin-angiotensin system, the sympathetic nervous system, growth factors, i.e. platelet-derived growth factor and insulin-like growth factor-I, C-reactive protein, and dyslipemia, on the other hand, factors well known to be involved in the atherogenic process, as well as for epidemiologic studies investigating the relationship between high-carbohydrate diets and the development of cardiovascular disease.

RESULTS

High-carbohydrate nutrition is shown to have the ability to induce vascular inflammation and plaque formation through an insulin-mediated activation of the RAS, growth factors, cytokines, the SNS, and C-reactive protein and to cause an atherogenic lipid profile in normal humans. Epidemiologic studies as well as studies in experimental animals corroborate an important role of dietary carbohydrate in atherogenesis.

CONCLUSION

High-carbohydrate diets, particularly in the form of high-glycemic index carbohydrate, have the ability to directly induce atherosclerosis. Based on anthropologic facts, the reason for these dietary-induced, insulin-mediated, atherogenic metabolic perturbations are suggested to be an insufficient adaptation to starch and sugars during human evolution. Restriction of insulinogenic food (starch and sugars) may help to prevent the development of atherosclerosis, one of the most common and costliest human diseases.

The effect of nutritional manipulation on ultra-endurance performance: a case study

The Atlantic Rowing Race requires teams of two to cover 3,000 nautical miles over 40-90 days. During this ultra-endurance event, competitors require substantial energy intake to meet metabolic requirements; therefore, sufficient physiological and nutritional support is paramount. Two highly trained males (aged 46) engaged in two 14d dietary interventions, with a 14d recovery period in between, to investigate the effect of such interventions on physiological (cardiovascular, cardiorespiratory, and blood-based measures) and performance-based (distance and split time) parameters during an ultra-endurance (2h on 2h off, for 24h) laboratory-based rowing protocol at 60% VO2max. Diet 1: high fat (HF) [60% fat, 30% carbohydrate and 10% protein] and Diet 2: high carbohydrate (HC) [20%, 70% and 10% respectively]. A greater distance was rowed by both subjects (155, 329 m and 134, 797 m vs 130, 089 m and 122, 112 m) with a concomitant reduced heart rate, volume of oxygen uptake, and respiratory exchange ratio, following the HF as opposed to HC dietary intervention. In summary, ultra-endurance performance was enhanced following a 14d HF diet, without apparent implications on liver function and overall lipid profile.

Lipids, lipoproteins, and exercise

PURPOSE

Dose-response relationships between exercise training volume and blood lipid changes suggest that exercise can favorably alter blood lipids at low training volumes, although the effects may not be observable until certain exercise thresholds are met.

METHODS AND RESULTS

Plasma triglyceride reductions are often observed after exercise training regimens requiring energy expenditures similar to those characterized to increase high-density lipoprotein cholesterol (HDL-C). Thresholds established from cross-sectional and longitudinal exercise training studies indicate that 15 to 20 miles/week of brisk walking or jogging, which elicit between 1,200 to 2,200 kcals of energy expenditure per week, is associated with triglyceride reductions of 5 to 38 mg/dL and HDL-C increases of 2 to 8 mg/dL. Exercise training seldom alters total cholesterol and low-density lipoprotein cholesterol (LDL-C) unless dietary fat intake is reduced and body weight loss is associated with the exercise training program, or both. Thus, for most individuals, the positive effects of regular exercise are exerted on blood lipids at low training volumes and accrue so that noticeable differences frequently occur with energy expenditures of 1,200 to 2,200 kcals/week.

CONCLUSIONS

It appears that weekly exercise caloric expenditures that meet or exceed the higher end of this range are more likely to produce the desired lipid changes. Regarding hyperlipidemic disorders, the primary means for intervention is pharmacologic, whereas diet modification, weight loss, and exercise, although important, are viewed as adjunctive therapies. Because much is known about the exercise training-induced plasma lipid and lipoprotein modifications as well as the mechanisms responsible for these changes, rehabilitation professionals can better develop a comprehensive medical management plan that optimizes pharmacologic, reduced dietary fat intake, weight loss, and exercise interventions.

Exercise in the treatment of lipid disorders

As a result of scientific evaluation, we know that exercise has a positive impact on the lipid and lipoprotein profile, and we have a greater understanding for the necessary amount of exercise needed to cause these changes. In the case of hyperlipidemic disorders, we know the primary means for intervention is pharmacological, and that diet, weight loss, and exercise are viewed as adjunctive therapies. Because much is known about the exercise training-induced plasma lipid and lipoprotein modifications as well as the lipoprotein enzyme changes, future research should continue to focus on the molecular basis for these changes. For example by knowing a person's apo E genotype, we gain better comprehension as to why some individuals respond to exercise, while others do not. Another area for further investigation is the assessment of drug and exercise interaction. Presently, little is known regarding the use of lipid-lowering drugs and the impact of exercise. Finally, these investigations could provide new insights for better understanding the exercise CAD protective effects. The future challenge is to better understand the impact that regular exercise participation has in optimizing the lipid and lipoprotein profile with individuals with special lipid disorders.

Fiber type dependent upregulation of human skeletal muscle UCP2 and UCP3 mRNA expression by high-fat diet

OBJECTIVE

To test the hypothesis that consumption of a high-fat diet leads to an increase in UCP mRNA expression in human skeletal muscle. In a group of endurance athletes, with a range in fiber type distribution, we hypothesized that the effect of the high-fat diet on UCP2 and UCP3 mRNA expression is more pronounced in muscle fibers which are known to have a high capacity to shift from carbohydrate to fat oxidation (type IIA fibers).

DESIGN

Ten healthy trained athletes (five males, five females) consumed a low-fat diet (17+/-0.9 en% of fat) and high-fat diet (41.4+/-1.4 en% fat) for 4 weeks, separated by a 4 week wash-out period. Muscle biopsies were collected at the end of both dietary periods.

MEASUREMENTS

Using RT-PCR, levels of UCP2 and UCP3 mRNA expression were measured and the percentage of type I, IIA and IIB fibers were determined using the myofibrillar ATPase method in all subjects.

RESULTS

UCP3L mRNA expression tended to be higher on the high-fat diet, an effect which reached significance when only males were considered (P=0.037). Furthermore, diet-induced change in mRNA expression of UCP3T (r: 0.66, P=0.037), UCP3L (r: 0.61, P=0.06) and UCP2 (r: 0.70, P=0.025), but not UCP3S, correlated significantly with percentage dietary fat on the high-fat diet. Plasma FFA levels were not different during the two diets. Finally, the percentage of type IIA fibers was positively correlated with the diet-induced change in mRNA expression for UCP2 (r: 0.7, P=0.03), UCP3L (r: 0.73, P=0.016) and UCP3T (r: 0.68, P=0.03) but not with UCP3S (r: 0.06, NS).

CONCLUSION

UCP2 and UCP3 mRNAs are upregulated by a high-fat diet. This upregulation is more pronounced in humans with high proportions of type IIA fibers, suggesting a role for UCPs in lipid utilization.

Adaptation to a fat-rich diet: effects on endurance performance in humans

The focus of this review is on studies where dietary fat content was manipulated to investigate the potential ergogenic effect of fat loading on endurance exercise performance. Adaptation to a fat-rich diet is influenced by several factors, of which the duration of the adaptation period, the exercise intensity of the performance test and the content of fat and carbohydrate in the experimental diet are the most important. Evidence is presented that short term adaptation, < 6 days, to a fat-rich diet is detrimental to exercise performance. When adaptation to a fat-rich diet was performed over longer periods, studies where performance was tested at moderate intensity, 60 to 80% of maximal oxygen uptake, demonstrate either no difference or an attenuated performance after consumption of a fat-rich compared with a carbohydrate-rich diet. When performance was measured at high intensity after a longer period of adaptation, it was at best maintained, but in most cases attenuated, compared with consuming a carbohydrate-rich diet. Furthermore, evidence is presented that adaptation to a fat-rich diet leads to an increased capacity of the fat oxidative system and an enhancement of the fat supply and subsequently the amount of fat oxidised during exercise. However, in most cases muscle glycogen storage is compromised, and although muscle glycogen breakdown is diminished to a certain extent, this is probably part of the explanation for the lack of performance enhancement after adaptation to a fat-rich diet.

Dietary fats and immune status in athletes: clinical implications

Athletes are competitive, train at very high levels with inadequate rest, consume too few calories, avoid fats, and may be at increased risk of infections. The immune system is sensitive to both fat intake and intense exercise, suggesting that athletes may have suppressed immune function. It has been reported that many athletes consume about 25% fewer calories than the estimated expenditure, leading to low intakes of some essential micronutrients and fats. Acute exercise has been shown to increase inflammatory and decrease antiinflammatory immune factors and may increase oxidant stress. Chronic exercise appears to improve immune competence. Lipids are powerful mediators of the immune system, and they may modulate the immunosuppressive effects of strenuous exercise. Studies have shown that a low-fat high-carbohydrate diet (15% fat, 65% CHO, 20% protein of total calories), typically eaten by athletes, increases inflammatory and decreases antiinflammatory immune factors, depresses antioxidants, and negatively affects blood lipoprotein ratios. Increasing total caloric intake by 25% to match energy expenditure and the dietary fat intake to 32% in athletes appears to reverse the negative effects on immune function and lipoprotein levels reported on a low-fat diet. Increasing the dietary fat intake of athletes to 42%, while maintaining caloric intake equal to expenditure, does not negatively affect immune competency or blood lipoproteins, whereas it improves endurance exercise performance at 60-80% of VO2max in cyclists, soldiers, and runners. There is no evidence that higher fat intakes (up to 42% of total calories), in calorically balanced diets, increase the risk of cancer, but studies are needed to determine whether the beneficial effects of higher fat diets in athletes reduce their rate of infections.

The effect of medium-chain triacylglycerols on the blood lipid profile of male endurance runners

Medium-chain triacylglycerol (MCT) oil is currently marketed for athletes as an ergogenic aid for optimal performance. Research assessing the blood lipid response of humans to MCT consumption is very limited and inconclusive. In this randomized cross-over study, male endurance runners (aged 30.5 +/- 5.5 years) were instructed to consume a low-fat diet (approximately 15% of energy) and consume either supplemental MCT oil (30 g twice each day) or long-chain triacylglycerol (LCT) oil (28 g corn oil twice each day) for 14 days. Each dietary trial was separated by at least 3 weeks. At the end of each trial, fasting blood samples were collected and analyzed for serum concentrations of total cholesterol (TC), high density lipoprotein-cholesterol (HDL-C), low density lipoprotein-cholesterol (LDL-C), and triacylglycerol (TG). Concentrations of TC (3.83 +/- 0.12 vs. 3.41 +/- 0.15 mmol/L, P = 0.004), LDL-C (1.76 +/- 0.12 vs. 1.51 +/- 0.14 mmol/L, P = 0.033), and TG (1.26 +/- 0.14 vs. 0.98 +/- 0.12 mmol/L, P = 0.006) were higher following the MCT trial than following the LCT trial, respectively. HDL-C concentration did not differ significantly between trials (MCT 1.48 +/- 0.05 mmol/L vs. LCT 1.45 +/- 0.04 mmol/L, P = 0.465). Although blood lipids remained within desirable ranges established by the National Cholesterol Education Program, these results suggest that consumption of MCT oil for 2 weeks negatively alters the blood lipid profile of athletes. Future studies should determine the effects of longer periods of MCT supplementation on serum lipids of exercisers and other groups of individuals. With little data suggesting that MCT are ergogenic, the adverse effects of MCT on blood lipid concentrations may outweigh any proposed benefits for athletes.

Influence of low and high dietary fat on physical performance in untrained males

PURPOSE

Dietary manipulations have been used in athletes to enhance aerobic performance. We intended to verify whether the quality of energy substrate provided by food (percentage of total calories from fat and carbohydrates) per se has the ability to affect aerobic performance in sedentary humans.

METHOD

Fourteen healthy sedentary males were sequentially submitted to 4-wk eucaloric diets (spontaneous diet: 30% of total calories from fat; low-fat, 15% fat; high-fat, 55% fat; and spontaneous, 30% fat). After each diet period, individual body mass, percentage body fat (plicometry), VO2max (incremental bicycle-ergometry) and endurance (pedaling time to exhaustion at 75%VO2max) were measured. VO2, VCO2, VE, R, and heart rate (HR) were measured at rest and during exercise tests. Body composition and performance data (VO2max and endurance) were compared for significant differences by repeated measures ANOVA.

RESULTS

Subjects' body weight, percentage body fat, and fitness status (indicated by intercept and slope of the HR/VO2 linear relationship) did not change significantly during the study, thus ruling out the influence of these potential confounders. For a given workload, VO2, VE, and R were unaffected by diet composition. VO2max and endurance time were not significantly modified by the different diets.

CONCLUSIONS

Our study showed no impact, positive or negative, of diet's macronutrient composition on physical performance. It appears that the quality of energy substrate provided by food does not have the ability to affect either maximal or submaximal aerobic performance in untrained individuals.

Utilization of lipids during exercise in human subjects: metabolic and dietary constraints

During endurance exercise, skeletal muscle relies mainly on both carbohydrate (CHO) and fat oxidation to cover energy needs. Numerous scientific studies have shown that increasing the exercise intensity leads to a progressive utilization of CHO. The latter will induce a state of glycogen depletion which is generally recognized as being a limiting factor for the continuation of strenuous exercise. Different dietary interventions have been proposed to overcome this limitation. A high-CHO diet during periods of intense training and competition, as well as CHO intake during exercise, are known to maintain a high rate of CHO oxidation and to delay fatigue. However, it has been recognized also that enhancing fatty acid (FA) oxidation during exercise induces a reduced rate of glycogen degradation, resulting in an improved endurance capacity. This is most strikingly observed as a result of frequent endurance exercise which improves a number of factors known to govern the FA flux and the oxidative capacity of skeletal muscle. Such factors are: (1) blood flow and capillarization; (2) lipolysis of triacylglycerol (TAG) in adipose tissue and circulating TAG and transport of FA from blood plasma to the sarcoplasm; (3) availability and rate of hydrolysis of intramuscular TAG; (4) activation of the FA and transport across the mitochondrial membrane; (5) the activity of enzymes in the oxidative pathway; (6) hormonal adaptations, i.e. sensitivity to catecholamines and insulin. The observation that the plasma FA concentration is an important factor in determining the rate of FA oxidation, and that some dietary factors may influence the rate of FA supply to muscle as well as to the mitochondria, has led to a number of dietary interventions with the ultimate goal to enhance FA oxidation and endurance performance. It appears that experimental data are not equivocal that dietary interventions, such as a high-fat diet, medium-chain TAG-fat emulsions and caffeine intake during exercise, as well as L-carnitine supplementation, do significantly enhance FA oxidation during exercise. So far, only regular endurance exercise can be classified as successful in achieving adaptations which enhance FA mobilization and oxidation.

Influence of the level of dietary lipid intake and maximal exercise on the immune status in runners

Chronic exercise and high fat diets are associated with immune suppression. This study compares cellular immune responses at rest and after maximal exercise in runners after eating diets comprised of 17% low fat (LF), 32% medium fat (MF), and 41% high fat (HF) (4 wk each). VO2max increased significantly from the 17% to 41% fat diet. The leukocyte cell counts were significantly increased after exercise. In men, significantly higher proliferative response to phytohemagglutinin (PHA) (P < 0.004) was observed with MF diet, while response to pokeweed mitogen (PWM) was significantly decreased by MF and HF diets. The number of CD8+ (suppressor) T cells was significantly higher in men and exercise increased it significantly, while CD4+ (helper) T cells were not affected. Natural killer cells number was significantly increased 2.5 fold by exercise and with increase in dietary fat. The production of IL-2 by peripheral blood mononuclear cells was significantly higher in men (P < 0.0001) and increasing dietary fat significantly increased IL-2 production (P < 0.001). In men, exercise decreased the level of the proinflammatory cytokines (IL-1, IL-6 and TNF-alpha), whereas in women, with the exception of MF diet for IL-6, exercise had no effect. This study indicates that short, intense bouts of exercise in runners training 40 miles.wk-1 have mixed effects on the immune system. A high percentage of fat intake (41%) did not have any deleterious effects on the immune system of the well-trained runners.