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Lemon (1) wrote an overview on protein metabolism and the effects of physical activity on protein requirements. He reviewed existing research on protein intake for strength athletes and endurance athletes, as well as addressed the possible negative health concerns of high protein diets. FINDINGS: Overall, research on strength athletes suggests that an optimal intake of protein for building muscle mass is 1.7-1.8 g/kg of bodyweight per day. The optimal intake for endurance athletes appears to be 1.2-1.4 g/kg of bodyweight per day. These recommendations are significantly greater than the RDA of .8 g/kg and are only valid if caloric needs are being met. These recommendations are also based upon research on college-aged males consuming adequate energy intake. Protein requirements may be different for individuals on lower calorie diets, females, individuals of different age groups (such as elderly individuals, children or adolescents experiencing rapid growth, or pregnant women), and individuals less likely to consume an optimal mixture of nutrients (such as vegetarians). The idea that high protein intakes can cause kidney problems appears to be a myth. This idea has been taken from research done on individuals with preexisting kidney disorders; however, such research cannot be extrapolated to healthy individuals. Numerous strength athletes consume diets extremely high in protein; if high protein diets caused kidney problems, one would see a much higher prevalence of kidney disorders in this population, which is not the case. In addition, animal studies utilizing very high protein intakes have not shown kidney problems. The increased nitrogen load placed upon the kidney by increased protein intake does not pose a potential threat to a healthy kidney. When protein intake is high, water loss may be increased due to the excretion of additional nitrogen. Individuals must ensure that water intake is high to prevent dehydration. The potential for high protein diets to increase calcium loss appears to be only a problem in purified protein. The high phosphate content of food protein negates any effect of protein on calcium. IMPLICATIONS: Strength athletes should consume 1.7-1.8 g/kg body weight of protein a day, and endurance athletes should consume 1.2-1.4 g/kg body weight of protein a day, assuming that caloric needs are being met. 1. Lemon, P.W. Is Increased Dietary Protein
Necessary or Beneficial for Individuals with a Physically Active
Lifestyle? Nutr. Rev. 54(4):S169-S175. 1996.
CARBOHYDRATE INGESTION/SUPPLEMENTATION FOR RESISTANCE EXERCISE AND TRAINING Conley et al (1) reviewed research on carbohydrate ingestion before, during, and after resistance training and the effects on performance and adaptations. FINDINGS: Not much research has been done on the effects of carbohydrate ingestion and its relationship to resistance training. It is not clear whether carbohydrate ingestion immediately prior or during a resistance training session can enhance performance; currently, most of the evidence suggest that it does not, unless the training session involves an extremely high volume of work, where carbohydrate availability may become a limiting factor. Carbohydrate ingestion during or immediately after a training session significantly increases postexercise insulin and gH levels, and can possibly suppress postexercise cortisol levels. This may have a beneficial effect on recovery and on protein synthesis and muscle hypertrophy. Research is needed to see whether an effect exists. IMPLICATIONS: A post-workout meal or beverage consisting of a large percentage of high-glycemic carbohydrates may be beneficial in enhancing recovery and may have a beneficial effect on increasing muscle size. 1. Conley, M.S. and M.H. Stone. Carbohydrate
Ingestion/Supplementation for Resistance Exercise and Training. Sports
Med. 21(1):7-17. 1996.
COST-EFFECTIVENESS OF PRE-EXERCISE CARBOHYDRATE MEALS AND THEIR IMPACT ON ENDURANCE PERFORMANCE Paddon-Jones et al (1) examined the effects of 4 different isocaloric carbohydrate meals 2 hours prior to 60-minute self-paced cycle ergometry trials. 8 trained male cyclists were used in the study. Each meal consisted of 460 kcal; the 4 meals administered to the cyclists were as follows:
Cost of the meals ranged from $.50 to $2.60. The ergometry trials were done in a random order over 4 weeks. Exercise and diet were standardized prior to each trial. The researchers measured distance traveled, blood glucose concentration, respiratory exchange ratio, oxygen consumption, and heart rate during each trial. FINDINGS: No significant differences were found between groups for any measurements. IMPLICATIONS: High-cost sports bars have no significant effects on endurance performance over a standard cereal meal 2 hours prior to endurance exercise. Athletes can save money by eating a carbohydrate based cereal prior to exercise without any detrimental effect on performance. 1. Paddon-Jones, D.J., and D.R. Pearson. Cost-effectiveness
of pre-exercise carbohydrate meals and their impact on endurance
performance. J. Strength and Cond. Res. 12(2):90-94.
1998.
In a double-blind crossover study, Lemon et al (1) examined protein requirements of novice bodybuilders undergoing an intensive strength training program. 12 untrained subjects received either an isoenergetic protein supplement or a carbohydrate supplement for 1 month while undergoing an intense, 6 day per week, 1.5 hour per day strength training program that was supervised by experienced bodybuilders. The 2 1-month treatment periods were separated by a 7 day washout period. Subjects receiving the protein supplement ingested 2.62 g of protein per kg bodyweight per day, while subjects receiving the carbohydrate supplement ingested 1.35 g/kg. Nitrogen balance, voluntary and electrically evoked strength, creatinine excretion, muscle area (measured by CAT scan), and biceps nitrogen content were measured. FINDINGS: On the basis of 3-day nitrogen balance measurements after 3.5 weeks on each treatment, the protein intake necessary to achieve zero nitrogen balance was approximately 1.4-1.5 g/kg per day. Based on these results, the recommended intake was 1.6-1.7 g/kg per day. No significant differences were found between groups for any measurements, although nitrogen balance was significantly more positive in the group ingesting 2.62 g/kg of protein per day. Subjects ingesting 1.35 g/kg of protein per day were in a negative nitrogen balance. IMPLICATIONS: In novice bodybuilders, increasing protein intake from 1.35 g/kg per day to 2.62 g/kg per day does not result in enhanced gains in strength or muscle size over a 1 month period. Further research is necessary to determine whether enhanced gains will occur over a longer period of time. The nitrogen balance for subjects receiving only 1.35 g/kg per day was negative, indicating that these subjects needed to ingest more protein. Since an intake of 1.4-1.5 g/kg was necessary to achieve a zero nitrogen balance, a protein intake of 1.6-1.7 g/kg bodyweight per day should be sufficient for strength athletes undergoing an intensive strength training program. 1. Lemon, P.W.R., M.A. Tarnopolsky, J.D. MacDougall, and S.A. Atkinson. Protein requirements and muscle mass/strength changes during intensive training in novice bodybuilders. J. Appl. Physiol. 73(2):767-775. 1992.
INFLUENCE OF HIGH AND LOW GLYCEMIC INDEX
MEALS ON ENDURANCE RUNNING CAPACITY
Wee et al (1) took 5 male and 3 female recreational runners and required them to run to exhaustion at 70% VO2 max on a treadmill. They were tested on 2 separate occasions performed 1 week apart. On one occasion and after an overnight fast, subjects were fed a high-glycemic carbohydrate meal 3 hours before exercise. On the other occasion, subjects were fed a low-glycemic carbohydrate meal. Both types of meals supplied 2 g of carbohydrate for each kilogram of the subjects' body weight, and no difference existed between the protein and fat content of each meal. Fasting blood and expired air samples were collected before the test meal was eaten. Blood samples were also taken 15 minutes, 30 minutes, and at 1, 2, and 3 hours after the meal. Resting expired air was measured every 30 minutes. During exercise, blood and expired air samples were taken every 20 minutes. Air samples were used to measure carbohydrate and fat oxidation. Blood samples were used to measure various factors including insulin, free fatty acids, and blood glucose. FINDINGS: Blood glucose peaked at 15 minutes after consumption of the high-glycemic meal and returned to a fasting level at 3 hours. Blood glucose did not significantly change when a low-glycemic meal was eaten. Serum insulin peaked at 15 minutes after consumption of the high-glycemic meal, increasing 10 times over fasting values. It was still 210% higher than fasting values at the beginning of exercise. In constrast, serum insulin rose slowly after the low-glycemic meal, rising to 80-160% above fasting levels. Serum free fatty acids and plasma glycerol decreased after both meals, but were significantly higher after consumption of a low-glycemic meal as compared to the high-glycemic meal. Rates of carbohydrate oxidation were higher after the high-glycemic meal. 49% more carbohydrate was oxidized during the 3 hours after the high-glycemic meal, and 69% more fat was oxidized after the low-glycemic meal. During exercise, time to exhaustion was similar between both types of meals. The rate of perceived exertion was lower at 60 minutes into exercise after the low-glycemic meal. After the low-glycemic meal, blood glucose was similar throughout exercise to pre-exercise levels. After the high-glycemic meal, blood glucose fell rapidly 20 minutes into exercise to values lower than at the start of exercise. However, no subjects reported symptoms of hypoglycemia. The low blood glucose increased after 20 minutes. Serum free fatty acids and plasma glycerol was significantly higher during exercise after the low-glycemic meal. The total amount of carbohydrate utilized during exercise was higher after ingestion of the high-glycemic meal. During exercise, carbohydrate oxidation was 12% lower and fat oxidation was 118% higher after ingestion of the low-glycemic meal. Total energy expenditure was the same between trials. IMPLICATIONS: Despite the popular recommendation to consume low-glycemic carbohydrates before exercise, it does not appear that the type of carbohydrate eaten 3 hours before exercise has any effect on endurance performance. However, this study does indicate the importance of consuming low-glycemic meals when fat loss is the goal. Subjects oxidized significantly less fat during rest and exercise after eating a high-glycemic meal. The main reason for this is that the rapid rise in blood sugar caused by eating a high-glycemic meal causes a rapid response in insulin, which was shown in the study. The higher insulin levels make fat loss more difficult since insulin shuts down fat oxidation. Thus, people interested in fat loss should stick with low-glycemic carbohydrates and eat 5-6 small meals (rather than the usual 2-3 large ones that many people have) to keep insulin levels lower and more steady throughout the day. The Glycemic Index is a website which explains the glycemic index and also gives a list of foods and their GI values. Maintenance of insulin levels also has important health implications. Chronic consumption of high-glycemic foods, combined with a lack of exercise, can result in chronically high levels of insulin, which can eventually lead to insulin insensitivity and Type 2 diabetes. 1. Wee, S.-L., C. Williams, S. Gray, and J. Horabin. Influence of high and low glycemic index meals on endurance running capacity. Med. Sci. Sports Exerc. 31(3):393-399. 1999.
Oliver (1) reviewed research on different types of dietary fats and their effect on the risk of ischemic heart disease. FINDINGS: A number of epidemiologic surveys have found a positive relationship between dietary fat intake and ischemic heart disease. This has led to the assumption that reduction in total fat intake, especially saturated fat intake, will reduce one's risk of ischemic heart disease. However, controlled clinical trials have not been able to support this idea. Also, a large long-term study examining the effect of reducing total and saturated fat intake on the risk of heart disease has not been done. Out of 6 studies looking at low-saturated fat, low-cholesterol diets in high-risk people, 4 found no significant reduction in the risk for heart disease (one found an adverse effect). 2 studies found a significant beneficial effect on heart disease risk by dramatically decreasing the intake of saturated fats and also dramatically increasing the amount of unsaturated fats, achieving a high polyunsaturated fat to saturated fat ratio (1.48 in one study and 1.01 in the other). 2 secondary prevention trials have looked at reducing total and saturated fat intake in people with existing heart disease. Neither study found an effect of reducing total and saturated fat intake on incidence of ischemic heart disease, although these studies were small and lacked statistical power. 6 studies have looked at altering the quality of dietary fat in heart disease patients by increasing the intake of polyunsaturated and monounsaturated fats. Only one of these studies found no effect on rates of nonfatal heart attacks and cardiac deaths. 2 studies have found supplementation with omega 3 fatty acids (from fish oils) cause significant reductions in the risk for ischemic heart disease and all-cause mortality. Long-term research on the American Heart Association Step 1 diet (<30% kilocalories from fat, <300 mg cholesterol/day, and a polyunsaturated/saturated fat ratio of 1.0) has been found to be ineffective at significantly reducing total or LDL cholesterol in free-living populations. The AHA Step 2 diet has been found to be more effective, but compliance is poor since it is so stringent (polyunsaturated/saturated fat ratio > 1.4 and cholesterol < 200 mg/day). Overall, studies which have increased the polyunsaturated to saturated fat ratio to greater than 1.0 have achieved reductions of serum cholesterol in the region of 15%. IMPLICATIONS: It is more important to increase the intake of polyunsaturated and monounsaturated fats while decreasing the intake of saturated fats (to achieve a high polyunsaturated fat to saturated fat ratio of > 1.0) rather than reduce total fat intake, saturated fat intake, and cholesterol in reducing the risk of heart disease. Good sources of polyunsaturated fats include flaxseed oil, canola oil, and safflower oil. Olive oil is a good source of monounsaturated fats. Supplementation with omega 3 fatty acids from fish oil can also help reduce heart disease risk. 1. Oliver, M.F. It is more important to increase the intake of unsaturated fats than to decrease the intake of saturated fats: evidence from clinical trials relating to ischemic heart disease. Am. J. Clin. Nutr. 66(suppl):980S-986S. 1997.
HIGH-OIL COMPARED WITH LOW-FAT, HIGH-CARBOHYDRATE DIETS IN THE PREVENTION OF ISCHEMIC HEART DISEASE Katan (1) reviewed the effects of low-fat, high-carbohydrate diets and low-saturated fat, high-unsaturated fat diets on coronary risk. While widespread agreement exists that a high-saturated fat diet increases heart disease risk, there is disagreement whether the reduction in saturated fat intake should be replaced by an increase in carbohydrate consumption or an increase in unsaturated fat consumption. FINDINGS: Replacement of saturated fats with either carbohydrates or monounsaturated fats lowers total cholesterol about the same amount. Omega 6 polyunsaturated fats cause an additional lowering of total cholesterol. Controlled studies have also found a diet with a high ratio of polyunsaturated fats to saturated fats helps prevent heart disease. When one lowers the amount of saturated fats and partially hydrogenated fats in the diet, the calories lost must be made up from another source. Three sources that can replace saturated fats are protein, carbohydrates, and unsaturated fats. Replacement of saturated fats by dietary protein lowers low-density-lipoprotein (LDL) concentrations without raising very-low-density lipoprotein (VLDL) concentrations and without reducing high-density lipoprotein (HDL) concentrations. However, a high protein diet may increase the risk of osteoporosis by possibly increasing calcium loss. Studies have consistently found that a high-carbohydrate, low-fat diet decreases total cholesterol, but part of his decrease is a fall in HDL. Since both LDL and HDL are lowered, the ratio of HDL to LDL remains unchanged and thus the risk of heart disease is not changed. Research has demonstrated that this effect is not transient and also occurs with both simple and complex carbohydrates. Research replacing saturated fats with unsaturated fats has consistently found an increase in the HDL to LDL ratio, reducing the risk of heart disease. The relationship between HDL and heart disease is extremely important. A very strong inverse relationship between HDL and heart disease risk has been consistently found, i.e. as HDL levels go up, heart disease risk goes down, and vice versa. Anything which reduces HDL will increase the risk of heart disease. Thus, a high-carbohydrate diet may potentially have an adverse effect on heart disease risk. It is possible that a high-carbohydrate, low-fat diet may have other benefits to offset the decrease in HDL. One possible benefit is weight loss. However, long-term studies of these diets on weight loss have not been very impressive, with only small decreases in body weight of 0.4-2.6 kg (.8-5.72 lbs). This reduction in weight was not sufficient to compensate for the decreased HDL. Even research on obese subjects with very large amounts of weight loss found only a very small increase in HDL for the weight lost. It was estimated that a 12.5 kg (27.5 lb) loss in body weight would be needed to compensate for the lowered HDL that would result from a 10% increase in carbohydrate intake. IMPLICATIONS: A diet low in saturated fat and high in unsaturated fat may be more beneficial in preventing the risk of heart disease than a diet low in fat and high in carbohydrate. This viewpoint is supported by epidemiological evidence of people that consume a Mediterranean diet, which is high in unsaturated fat and low in saturated fat; people that consume this type of diet have been shown to have very low rates of heart disease. 1. Katan, M.B. High-oil compared with low-fat, high-carbohydrate diets in the preventioin of ischemic heart disease. Am. J. Clin. Nutr. 66(suppl):974S-979S. 1997.
Grundy (1) reviewed the effects of different types of fats on serum cholesterol concentrations. FINDINGS: Dietary saturated fatty acids, specifically palmitic acid, myristic acid, and lauric acid, raise serum cholesterol. These saturated fatty acids make up about 2/3 of the saturated fatty acids in the American diet. One saturated fatty acid, stearic acid, does not raise serum cholesterol. Monounsaturated fatty acids, such as oleic acid, neither raise nor lower serum cholesterol, although oleic acid will reduce the number of circulating LDL particles. Carbohydrates raise VLDL cholesterol, reduce HDL, and reduce LDL by reducing the cholesterol content of LDL particles and not by reducing the number of circulating LDL particles. trans monounsaturated fatty acids raise LDL-cholesterol and also may have a small HDL-lowering effect. Linoleic acid, a polyunsaturated fatty acid, will lower total and LDL-cholesterol concentrations. However, large amounts of this fatty acid should not be consumed, since high intakes may increase cancer risk as well as increase the susceptibility of LDL to oxidation, increasing the risk of heart disease. IMPLICATIONS: To reduce the risk of heart disease and cancer, intake of animal fats and trans fatty acids (partially hydrogenated fats) should be reduced and should not make up more than 7-8% of total caloric intake. Polyunsaturated fats high in linoleic acid should not make up more than 7% of total caloric intake. The remaining intake from fat (about 15-16% of total kilocalories) should come from mainly monounsaturated fatty acids, such as oleic acid in olive oil. People in the Mediterranean consume large amounts of oleic acid and have very low rates of heart disease and cancer. 1. Grundy, S.M. What is the desirable ratio of saturated, polyunsatruated, and monounsaturated fatty acids in the diet? Am. J. Clin. Nutr. 66(suppl):988S-990S. 1997.
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