High-carbohydrate versus high-fat diets: effect on body composition in trained cyclists

The Effects of Hyperhydrating Supplements Containing Creatine and Glucose on Plasma Lipids and Insulin Sensitivity in Endurance-Trained Athletes

The addition of carbohydrate (CHO) in the form of simple sugars to creatine (Cr) supplements is central. The study aimed to determine whether ingestion of glucose (Glu) simultaneously with Cr and glycerol (Cr/Gly) supplement is detrimental to plasma lipids of endurance-trained individuals and find out whether modification arising can be attenuated by replacing part of the Glu with alpha lipoic acid (Ala). Twenty-two endurance-trained cyclists were randomized to receive Cr/Gly/Glu (11.4 g Cr-H₂O, 1 g Gly/kg BM, and 150 g Glu) or Cr/Gly/Glu/Ala (11.4 g Cr-H₂O, 1 g Gly/kg BM, 100 g Glu, and 1 g Ala) for 7 days. Fasting concentration of TAG increased significantly (P < 0.01) after supplementation with Cr/Gly/Glu (before: 0.9 ± 0.2 mmol/L; after: 1.3 ± 0.4 mmol/L) and Cr/Gly/Glu/Ala (before: 0.8 ± 0.2 mmol/L; after: 1.2 ± 0.5 mmol/L) but changes were not different between the groups. Supplementation significantly (P < 0.05) increased the TAG to HDL-cholesterol ratio but had no effect on fasting concentration of total, HDL-, and LDL-cholesterol and insulin resistance. Thus, addition of Glu to Cr containing supplements enhances plasma TAG concentration and the TAG to HDL-cholesterol ratio and this enhancement cannot be attenuated by partial replacement of Glu with Ala.

Cycling and bone health: a systematic review

BACKGROUND

Cycling is considered to be a highly beneficial sport for significantly enhancing cardiovascular fitness in individuals, yet studies show little or no corresponding improvements in bone mass.

METHODS

A scientific literature search on studies discussing bone mass and bone metabolism in cyclists was performed to collect all relevant published material up to April 2012. Descriptive, cross-sectional, longitudinal and interventional studies were all reviewed. Inclusion criteria were met by 31 studies.

RESULTS

Heterogeneous studies in terms of gender, age, data source, group of comparison, cycling level or modality practiced among others factors showed minor but important differences in results. Despite some controversial results, it has been observed that adult road cyclists participating in regular training have low bone mineral density in key regions (for example, lumbar spine). Conversely, other types of cycling (such as mountain biking), or combination with other sports could reduce this unsafe effect. These results cannot yet be explained by differences in dietary patterns or endocrine factors.

CONCLUSIONS

From our comprehensive survey of the current available literature it can be concluded that road cycling does not appear to confer any significant osteogenic benefit. The cause of this may be related to spending long hours in a weight-supported position on the bike in combination with the necessary enforced recovery time that involves a large amount of time sitting or lying supine, especially at the competitive level.

Thermodynamics and metabolic advantage of weight loss diets

Published reports show that low carbohydrate weight loss diets provide a metabolic advantage, a greater weight loss per calorie consumed compared to isocaloric high carbohydrate diets. These reports have not been refuted but rather largely ignored, presumably because of the apparent violation of the laws of thermodynamics ("a calorie is a calorie"). In this review, we show that there is no such violation of thermodynamic laws. Energy utilization of different diets depends on the chemical pathway taken and a metabolic analysis of the efficiency of different pathways reveals large differences. Likewise, thermogenesis produced by diets of different macronutrient composition varies widely. We present a plausible mechanism that depends on the inefficiency of metabolic cycles and, in particular, protein turnover. A low carbohydrate diet makes demands on protein turnover for gluconeogenesis. From a theoretical point of view,energy balance between two diets is to be expected only if the subjects have the same final physiologic state, and only if all of the changes contributing to the energy, heat, work and chemical effects are known. Most diet experiments do not conform to this ideal. There is no theoretical contradiction in metabolic advantage and no theoretical barrier to accepting reports describing this effect.

Low-fat diet alters intramuscular substrates and reduces lipolysis and fat oxidation during exercise

We determined whether a low-fat diet reduces intramuscular triglyceride (IMTG) concentration, whole body lipolyis, total fat oxidation, and calculated nonplasma fatty acid (FA) oxidation during exercise. Seven endurance-trained cyclists were studied over a 3-wk period during which time they exercised 2 h/day at 70% of maximum O2 uptake VO(2 max) and consumed approximately 4,400 kcal/day. During the 1st wk, their fat intake provided 32% of energy. During the 2nd and 3rd wk, they were randomly assigned to eat 2 or 22% of energy from fat (2%FAT or 22%FAT). Compared with 22%FAT, 2%FAT lowered IMTG concentration and raised muscle glycogen concentration at rest (P < 0.05). Metabolism was studied during 1 h of exercise at 67% VO(2 max) performed in the fasted state. 2%FAT resulted in a 27% reduction (P < 0.05) in total fat oxidation vs. 22%FAT without altering the stable isotopically determined rates of plasma free fatty acid or glucose disappearance. Therefore, 2%FAT reduced calculated nonplasma FA oxidation by 40% in association with a 19% reduction in whole body lipolysis while increasing calculated minimal muscle glycogen oxidation compared with 22%FAT (all P < 0.05). In summary, an extremely low fat (2% of energy) and high-carbohydrate diet lowers whole body lipolysis, total fat oxidation, and nonplasma FA oxidation during exercise in the fasted state in association with a reduced concentration of intramuscular triglyceride.

Energy and macronutrient intakes of elite figure skaters

OBJECTIVES

Dietary guidelines for athletes emphasize complex carbohydrates. This study examined dietary intakes of elite figure skaters relative to current recommendations in sports nutrition.

PARTICIPANTS

Subjects were male (n=80) and female (n=81) figure skaters taking part in a series of training camps held in Colorado between 1988 and 1995. Mean age was 18 years for men and 16 years for women.

DESIGN

Measures of height, weight, and skinfold thickness were used to calculate body mass index and percent body fat. Blood samples were drawn for analysis of nutritional status. Energy and nutrient intakes were based on 3-day food records.

STATISTICAL ANALYSES

Multivariate regression model and correlation analyses used the SPSS for Windows program.

RESULTS

Values of body mass index and percent body fat were similar to those obtained for elite athletes in other studies. Plasma chemistries were in the normal range. Energy intakes (2,329 kcal/day for men and 1,545 kcal/day for women) were below recommended values for sex and age. The skaters derived approximately 50% of their daily energy from sugars and fat. Sugars alone accounted for 25% of daily energy intakes--the skaters consumed between 100 g (women) and 142 g of sugars per day. Sugar and fat intakes, when expressed as percent of daily energy, were inversely linked, providing evidence of a fat-sugar seesaw. Higher-energy diets were higher in fat but lower in carbohydrate and protein.

APPLICATIONS

High consumption of sugars and fat by elite athletes was not associated with overweight or excess body fat. Although recommended diets are usually built around complex carbohydrates, dietetics professionals can address the increased energy needs of elite athletes by recommending energy-dense foods. Sugars and fats are efficient sources of energy per unit volume.