Friday, December 28, 2012

Feeding the Female Athlete:Nutritional requirements for strength-training women by Jerry Brainum

A recently published comprehensive review examined the nutritional requirements of women who regularly engaged in bodybuilding, powerlifting and/or weightlifting. While many of their nutritional requirements are similar to those of men, there are a few notable differences.
    Women often initially show greater strength gains because they’re usually weaker than men at the start of a training program. Another obvious difference between the sexes is the ultimate degree of attainable muscle size. Because of both structural and hormonal differences, the average man can develop far larger muscles than the average woman. That’s most often attributed to men’s higher level of testosterone. Women won’t develop a masculine body shape—unless, of course, they use testosterone-based drugs and other anabolic substances associated with muscle bulk. (The fact that women respond to such drugs is evident from the appearance of some competitive female bodybuilders, whose muscular size far exceeds what could be developed through natural means.) Women who choose the natural route can still attain a significant loss of bodyfat and muscular definition, though it’s admittedly an uphill battle in comparison to males because a woman’s hormonal profile—higher estrogen, lower testosterone—tends to favor fat accretion, especially in the lower body and just under the skin.
    From the standpoint of exercise metabolism, women show a clear superiority in fat use over men—again, likely the result of higher estrogen. When engaged in exercise, women can tap into fat stores more efficiently and rapidly than men. The performance gap between men and women is far less significant in endurance than strength sports.
     Women store higher levels of fat in muscle, known as intramuscular triglyceride. IMTG is believed to be related to a woman’s higher percentage of slow-twitch muscle fibers, also known as “endurance” fibers, which preferentially burn more fat during activity and at rest. Studies of endurance exercise show that women tap into IMTG at greater levels than men.
    The greater use of fat spares muscle glycogen, which is stored carbohydrate, an effect that extends to weight training, with women using more fat and less glycogen. It’s attributed to a lower activity of the glycolytic enzymes in muscle that activate muscle glycogen breakdown, which may be due to higher estrogen levels.
     Because of their concern with appearance, many women overly restrict calorie intake, which some studies show can work against elite female athletes. Overly restricting calories leads to a lower metabolic rate, which paradoxically increases bodyfat levels. A low energy intake also leads to fatigue, irritation and decreased performance—as it does in men.
     Women who don’t eat enough show decreased thyroid hormone activity, which not only depresses fat losses but also results in lower energy. Bone mass, fertility and creatine replenishment in muscle are also adversely affected. Not consuming enough food increases the risks of nutrient deficiencies.
Since weight training increases resting metabolic rate for up to 36 hours, women should get most of their calories before and after training. That keeps calories from shifting to bodyfat stores. From a practical standpoint, women engaged in weight training need to eat 39 to 44 calories per kilogram of bodyweight daily. Health and energy problems occur if an active woman’s total daily calories drop below 1,800.
     Studies confirm that women handle carbohydrates differently than men. Women not only use less glycogen during training but also synthesize less after a workout. To synthesize more glycogen following training, a woman must take in up to eight grams of carbohydrate per kilogram of bodyweight. That much carb, however, would use up a large percentage of her daily calories.
    Women do need carbohydrates for purposes of glycogen replenishment following training, but they don’t need to eat like endurance athletes. The best type of carbs are those with a low-glycemic rating, meaning that they provide a slower delivery of carbs into the body, favoring less fat synthesis. Foods high in fiber have lower glycemic index numbers—fruits, vegetables, brown rice, whole-grain breads, oatmeal, beans, legumes and sweet potatoes. Cruciferous vegetables, such as broccoli, brussels sprouts, kale, cabbage and bok choy, are particularly beneficial for women because they contain natural elements that lower excessive estrogen levels, thus helping women lose superfluous water and fat.
     Studies show that men burn more protein during training than women do. Women’s higher use of fat during exercise may provide a sparing effect on protein, as well as glycogen. On the other hand, studies also show that women are less efficient than men in promoting muscle protein synthesis after training. That points to a need to get more protein at that critical time. For building lean mass, women are advised to eat small amounts of high-quality, rapidly digested protein with some carbohydrate before and after exercise and between meals to maintain an optimal anabolic metabolic environment.
    Women are also advised to ignore the myths about high-protein diets, among them that eating a lot of protein leads to bone loss and osteoporosis. Studies show an opposite effect: A higher protein intake promotes bone mass. Some high-protein foods also provide nutrients essential to bone formation and maintenance, such as calcium, magnesium and vitamin D.
     Some women espouse vegetarianism in the belief that it’s both healthier than eating meat and favors less bodyfat. While it’s indeed possible to maintain health while forgoing animal proteins, that’s not ideal for bodybuilding. Women need to pay special attention to iron intake, since they’re more at risk for anemia. Meat contains the most easily absorbed source of iron, heme iron, while the iron contained in plant sources often isn’t as available, due to iron-blocking substances in plants, such as oxalate and phytate. Animal proteins also provide such vital nutrients as B-complex vitamins and minerals. Women who are worried about the fat content of meat can take a high-quality protein supplement such as whey and/or casein, which will be devoid of fat and carbs.
    Some women may also be overly concerned about fat, thinking that eating fat promotes bodyfat. A suitable fat intake helps replenish the intramuscular fat stores that women tap into during exercise, which also spares their limited muscle glycogen stores. Women should get 30 percent of their daily calorie requirement from fat to replenish depleted IMTG stores. If they don’t get enough dietary fat, those muscle fat stores can remain depleted for two days after training, adversely affecting exercise ability.
     Dietary fat is also required to maintain sex hormone function in women, just as it is in men. If a woman doesn’t eat enough fat, she’ll likely experience menstrual disturbances. Getting less than 15 percent of calories from fat also increases the risk of an essential fatty acid deficiency, which can result in diminished fat burning in addition to serious health problems.
   Dietary fats should come from lean protein foods, nuts, seeds, fatty fish such as salmon (or fish oil supplements for omega-3 if you hate eating fish), as well as flaxseed, safflower, canola and extra-virgin olive oils. Avoid trans fats—also known as partially hydrogenated fats—which favor bodyfat, cancer and cardiovascular disease, in addition to amino acid loss in muscle. Eating healthful fats permits a lower carb intake, favoring better body composition for female strength athletes.
    Women respond to most supplements like men. Creatine works well, although it doesn’t block protein oxidation as it does in men. It’s a moot point, though, since women burn less protein than men during exercise anyway. Women should also avoid all types of testosterone-boosting supplements, including the estrogen blockers. Such supplements are great for men, but in women they can create serious hormonal disturbances.
    DHEA acts as a hormone precursor in both men and women. In men it tends to convert into estrogen, but in women it always converts into testosterone. While that initially sounds good for female strength athletes, many of them have developed serious cases of acne when taking DHEA. That’s not so surprising if you consider that the DHEA spurt in teenagers of both sexes is what causes acne. A form of DHEA that doesn’t convert into sex hormones, 7-keto DHEA, is also available in supplement form. It may help prevent dieting plateaus by maintaining thyroid output, but it’s free of the adverse effects associated with regular DHEA.
Add it up, and it’s clear that women strength athletes should reduce carbohydrate intake in favor of “good” fat sources while increasing their protein, especially after training. Doing so ensures great progress while maintaining energy and health.   

Volek, J.S., et al. (2006). Nutritional aspects of women strength athletes. British J Sports Med. 40:742-48.

©,2013 Jerry Brainum. Any reprinting in any type of media, including electronic and foreign is expressly prohibited.

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