Sceptically Fit

23/06/2011

Female Athletes – eat more protein, eat less carbs

Filed under: Health and Nutrition — Tags: , , , , — Sceptically Me @ 17:14

I recently came across a study from 2006 looking at the dietary needs of women performing resistance exercises.  This study showed that women were less responsive to glycogen during exercise, less able to utilise carbohydrates for glycogen replenishment and required more protein then men post exercise. The advice from the study is that women should lower their carbohydrate consumption and increase protein and fat.

Nutritional aspects of women strength athletes

  • Less use of glycogen in women during resistance exercises (also sprints – yay HIIT)

For example, a repeated maximal knee extension protocol resulted in significant glycogen depletion in type I and II muscle fibres in trained and untrained men, but this was not found in women.An attenuated reduction in glycogen in women after resistance exercise is consistent with similar observations after sprint exerciseand may result from lower glycolytic enzyme activity in women or a suppressive effect of estradiol.This gender difference in carbohydrate metabolism during resistance exercise may also be explained by the fact that women usually have a greater capacity for lipid breakdown and oxidation compared to men, such that glycogen is spared more in women than in men.

  • Increased fat oxidisation post-exercise when doing resistance exercise rather than cardio. Carbohydrate demands post exercise are lower.

Immediately following resistance exercise in women, the respiratory exchange ratio (RER) significantly declines indicating an increase in fat oxidation during recovery.This significant decrease in RER post‐exercise has been noted by several investigators when resistance exercise was compared against sitting and against treadmill exercise with the same aerobic energy cost.  Elevations in fat oxidation post‐exercise spare exogenous carbohydrate for glycogen replenishment and underscore the importance of IMTG and dietary fat as an energy source.

  • Advice on carbohydrate consumption:

One reason that high carbohydrate diets are not optimal for women strength athletes relates to the finding that women use significantly less glycogen during resistance exercise than menand synthesise less glycogen in response to a given amount of dietary carbohydrate.

carbohydrates with low glycaemic indices should be chosen to reduce the risk factors for cardiovascular disease, stroke, and diabetes as observed in women who consume higher glycaemic carbohydrates. Low glycaemic carbohydrates are rich in dietary fibre and contain important micronutrients, such as iron and B vitamins. These micronutrients are commonly found to be suboptimal in diets of women athletesbased on evaluations of self‐reported food intake and some biochemical indices of mineral and vitamin status.Fruits, vegetables, brown rice, enriched whole grain breads, whole grain prepared cereals, rolled oats, beans, legumes, and sweet potatoes are good examples of low glycaemic carbohydrate foods that strength training women should consume.

  • Advice on protein consumption

Although studies are inconsistent with regards to gender differences in protein metabolism,there is some indication that leucine oxidation is greater in men, and women may oxidise less protein during exercise because they derive more of their exercise energy needs from fat.

An area of particular interest in protein nutrition is the concept of timing and the differences that may exist between genders. In contrast to men, women have an attenuated increase in muscle protein fractional synthetic rate when amino acids are provided after exercise, suggesting that women may need to consume more protein after resistance exercise in order to elicit the same anabolic environment.

  • Addressing health concerns of a high protein diet (quoted at length – my highlights)

High protein diets have long been criticised on the basis of deleterious effects on bone due to their greater acid load that requires neutralisation by calcium salts.Women are at increased risk of osteoporosis as they age, so any potential adverse effects on bone health should be avoided. However, the justification to limit protein based on this criticism may not be warranted. Using dual stable calcium isotopes to quantify calcium kinetics in women, Kerstetter et al found that a high protein diet did not have any negative effects on net bone balance. Further, a protein supplement (42 g protein, 24 g carbohydrate, 2 g fat) given to young women and men throughout a 6 month strength and conditioning program, increased insulin growth factor‐1 and serum bone alkaline phosphatase (indicating increased bone formation) compared to a carbohydrate supplement of equal caloric value. Dietary unprocessed sources of protein contain both calcium and phosphorus and can contribute to increased dietary calcium and phosphorus intake. High protein intake does not appear to have adverse consequences for bone health in females, but rather, may be beneficial. Another criticism of high protein diets is that habitual consumption in excess of recommended intakes promotes chronic renal disease through increased glomerular pressure and hyperfiltration. On the contrary, the effects of high protein diets consumed by healthy humans were recently reviewed and it was concluded that there is insufficient proof to limit protein intake for the purpose of preserving renal health in healthy adults. The Institute of Medicine has also concluded that there is no clear evidence indicating that high protein diets have other deleterious effects including increased risk of cancer or cardiovascular disease. The final most common criticism against high protein diets in relation to strength athletes is that increasing protein intake beyond the recommended level is unlikely to result in additional increases in lean tissue because there is a limit to the rate at which protein tissue can be accrued. The argument against this statement is that even if there is a limit to gains in lean mass with high protein ingestion, increasing evidence shows that dietary substitution of carbohydrate with protein results in a variety of favourable health effects including enhanced weight loss, reduction in truncal adipose tissue, optimal maintenance of blood glucose, and improved lipid profile.

  • Advice on fat consumption

women seem to rely less on glycogen for resistance exercise than men. Thus, high fat diets may be advantageous for women strength athletes to complement energy production derived from IMTG and circulating lipids while concurrently sparing muscle glycogen

Investigators have demonstrated that women endurance athletes in energy balance need to obtain at least 30% of their energy from dietary fat to ensure rapid replenishment of IMTG following exercise. If fat intake is sub‐optimal, there is continued IMTG depletion following exercise for up to 2 days, which may limit performance in subsequent exercise sessions.

Fat intake greater than 15% of energy from unprocessed sources may help to prevent the female athlete triad as its consumption will help attain energy balance, improve bone health, and avoid depressed sex hormone concentrations.

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