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The preoccupation of modern society with appearance is reflected in part by the preponderance of Americans who engage in dieting behaviors. Despite the nutritional and fitness literature which pervades society today, 33% of the American population continues to be overweight (Bates, 1997). The USDA recommendation for a low-fat, high-complex-carbohydrate diet over the years has seemingly not been effective, since the proportion of overweight Americans has increased. Many frustrated Americans have in turn looked beyond the high-carb, low fat diet to other less conventional measures (http.//web.usatoday.com/life/health/lhs641.htm). Dietary fads have sprouted over the years to meet this need for a novel approach to weight loss. Such programs deviate from the traditional dietary advice to consume 55% of calories from carbohydrates, 30% from fat, and 15% from protein. One alternative approach to weight loss that has received considerable attention is the high-protein diet. This type of diet and its underlying theories will be examined, as well as the validity of its weight-loss claims.
The basic premise of all high-protein diets is that weight loss occurs
from an increase in protein and a decrease in carbohydrates in dietary
composition . What differentiates high-protein diets today from earlier
ones in the 1970's is the assertion that loading up on carbohydrates results
in loading up of pounds (Albatross, 1997). High-carbohydrate diets are
postulated to disrupt hormonal balance by stimulating insulin production,
which in turn promotes glucose to be stored as fat in the body. Information
on three variations of high-protein diets will be reviewed, followed by
a scientific and nutritional analysis of these weight loss approaches.
The Zone diet, as described in The Zone by Barry Sears, Ph.D. is an example of a "protein-adequate diet" (http://web.usatoday.com/life/health/lhs641.htm). Small meals of fruits, vegetables, monounsaturated fats, and low-fat proteins are advised to be eaten throughout the day. Sources of total calorie composition outlined by this dietary plan is as follows: 40% carbohydrate, 30% fat, 30% protein. The amount of fat is dictated by the amount of protein consumed at each meal. The role of fat in this diet plan is described by Dr. Sears as follows: slows the rate of carbohydrate entry into bloodstream which reduces insulin response, releases hormone (CCK) from stomach to tell brain to stop eating, and supplies the building blocks (essential fatty acids) for eicosanoids (http://www.users.cts.com/crash/d/dbrowndc/zonefaq.htm#Unfavorable). Therefore according to this perspective, in order for the body to burn fat and weight loss to occur, insulin must be maintained within a prescribed zone (Kirby, 1997).
This high-protein diet is depicted as a life-long hormonal control program which allows a person to maximize full genetic potential. The zone diet allows a person to eat as if they were already at their ideal percentage of body fat because stored calories are being hormonally released. The advertised effects of this dietary plan on the body include: burns fat, fights heart disease, diabetes, PMS, chronic fatigue, depression, cancer, and alleviates painful symptoms associated with diseases such as multiple sclerosis and HIV (http://www.harpercollins.com/bsellers/zoneh.htm). The following items are noted to occur following participation in this weight loss regime: marked reduction in carbohydrate cravings and increased mental focus after 2 to 3 days, significant increase in lack of hunger plus better physical performance after 5 days, and clothes fitting noticeably better after 2 weeks (http://www.users.cts.com/crash/d/dbrowndc/zonefaq.htm#Unfavorable). However, problems have been raised in relation to the high-protein diet outlined by Barry Sears. Constipation, small portions, very few calories, concerns over excess protein, and disbelief over what constitutes bad food (e.g. carrots and bananas) are some of the issues brought against this high-protein diet (http://www.users.cts.com/crash/d/dbrowndc/darkside.htm).
A second high-protein diet that has been popularized for weight loss is from the book Protein Power, written by Drs. Michael and Mary Dan Eades (http://web.usatoday.com/life/health/lhs641.htm). Their plan works with the body's metabolic biochemistry, bringing hormones (including insulin) into balance. This regimen calls for eating a protein-rich, moderate-fat, low-carbohydrate diet. It is advertised not only to promote feeling better and more energetic within a week, but also to correct blood sugar levels, high blood pressure, and elevated cholesterol within 3 weeks (http://www.bdd.com/newrl/bddnewrl.cgi/02-01-96/prot). This high-protein diet is based on the notion that carbohydrate consumption increases blood glucose, and that excess carbohydrate leads to excess insulin which leads to obesity, high blood pressure, and heart disease (http://www.bdd.com/newrl/bddnewrl.cgi/02-01-96/prot_exrt).
A third high-protein diet that has gained attention is that of Dr. Atkins' New Diet Revolution, by Robert C. Atkins, M.D. This diet severely restricts carbohydrates in order to promote the burning of stored fat (http://web.usatoday.com/life/health/lhs641.htm). This high-protein diet also emphasizes the focal role of insulin in producing weight gain. Because of its carbohydrate restriction, this regimen has been accused of promoting a state of ketosis. Ketosis is when there are no glycogen reserves in the liver, when the body breaks down muscle mass in order to make carbohydrates that are necessary for brain function (http://www.users.cts.com/crash/d/dbrowndc/zonefaq.htm#Unfavorable). Ketosis causes dizziness, weakness, nausea and other problems, yet ironically has been a main selling point in Atkins' book.
A fundamental criticism of high-protein diets is the faulty assumption that high-carbohydrate diets have led to Americans become overweight (Alberts, 1997). Critics propose that a diet composed mostly of carbohydrates is not responsible for Americans becoming fatter, but rather increased calorie consumption and decreased exercise has led to weight gain (Bates, 1997). Therefore the "Food Guide Pyramid" (USDA dietary guidelines revised- 1990) which calls for 6 to 11 servings of bread, cereal, rice and pasta daily is not responsible for our national weight gain. Rather, the imbalance of energy intake over energy expenditure is responsible for Americans accumulating excess body fat.
The second criticism of high-protein diets concerns what exactly produces weight loss in persons who participate in these plans. Critics of high-protein diets propose that it is calorie restriction to which weight loss can be attributed, rather than to any theoretical underpinnings which advocates might suggest. High-protein diets are also criticized because they encourage loss of muscle mass as opposed to loss of body fat. This is because protein metabolism produces a by-product, nitrogen, which is toxic to the body and must be flushed out with water. The body attains this water by breaking down muscle tissue. Thereby rapid weight loss as a result of such a diet is usually due to changes in water balance, not loss of fat (Alberts, 1997).
A study by Vazeuez et.al (1995) investigated the independent effects of carbohydrate and protein on protein metabolism. Different compositions of carbohydrate and protein in very-low-energy diets (VLEDs) were examined to determine how they affected protein sparing during weight reduction. Losses of nitrogen (through urine excretion) during VLED treatment was found to be highest in subjects whose diet was composed of low carbohydrate/ low protein. The protein content of the VLED was found to be the significant factor affecting high urea nitrogen excretion.
An additional criticism of such popular protein diets is that the dietary composition (usually 1,000 kcal or less, with 50 mg of carbohydrates and 120g or more of protein) when combined with energy restriction, results in ketosis (Lissner et al., 1992). These diets do not contain enough carbohydrates to keep the body adequately fueled (brains operate on glucose which is best provided for by carbohydrates). In addition these diets are criticized by nutritionists for not providing fiber, discouraging fruits and vegetables, vitamin and mineral deficiencies, and running the risk of dehydration, nausea, and kidney problems (these are complications associated with staying on a high-protein, low carbohydrate diet for more than a couple of months) (Bates, 1997). Therefore, such fad diets with a high emphasis on protein are often nutritionally inadequate, scientifically unsound, and potentially dangerous (Brownell, 1987).
A third criticism of high-protein diets is aimed at its tenet concerning the central role that insulin plays in weight gain. Protein proponents claim that taking in more carbohydrates than immediately needed for energy will result in increased insulin secretion, which then results in insulin resistance and weight gain. However, there is a paucity of research evidence to support these claims. Although there is a correlation between insulin resistance and obesity, this correlation does not imply causation. It is more likely that people being overweight causes their insulin resistance, as opposed to becoming overweight as a result of excessive carbohydrate intake (Bates, 1997 ).
Cooney and Storlien (1994) review the relationship between insulin action, thermogenesis and obesity. They support the case of obesity as being a major cause of insulin resistance, yet also acknowledge that it is possible to be insulin resistant without being obese. They report that insulin resistance cannot lead to obesity via a decrease in thermogenesis (energy expenditure). This is supported by the fact that obese individuals do not appear to have lower metabolic rates then lean individuals. If insulin resistance did impair thermogenesis, then improving insulin action by weight loss should increase thermogenesis. This however, it does not do. Therefore high-carbohydrate intake does not cause insulin resistance, and thus is not a mechanism whereby people gain weight. This is one just illustration of how the protein-proponents' theory on the role of insulin in weight gain does not appear to be substantiated by the scientific literature.
Sharma (1992) acknowledges that insulin resistance exists in obese and non-obese individuals. Mechanisms whereby insulin resistance can be improved are reviewed, and many of these measures contradict the principles upon which high-protein diets are based. Insulin resistance is reported to be amenable in diabetic, obese, and normal humans by a diet rich in carbohydrates, fiber and also by exercise. These measures reduce the risk of cardiovascular disease, which is an additional area of concern in relation high-protein diets (Alberts, 1997). Similar associations between diet, insulin resistance and hypertension were found in a study by Prichard et al. (1992)
The previously listed studies and others have acknowledged that insulin resistance may be found in non-obese subjects. This occurrence can perhaps be explained by a genetic determinant of insulin action. This assumption is supported by data from the study of Bogardus et al.(1985) which compared differences between in vivo insulin action in Southwest American Indians and Caucasian males. This study documented degree of obesity to be negatively associated with insulin action, yet only half of the variability could be accounted for by differences in obesity and maximal aerobic capacity. Thus a direct link does not seem to exist between insulin levels and weight gain as high-protein diet supporters proclaim.
In light of the unfavorable nutritional analysis of high-protein diets
and their lack of support from the published scientific literature, it
seems safe to say that such diets are not advisable. The preoccupation
of society with appearance has forced many people to turn to such fad diets
out of frustration from not achieving their weight loss goals. However,
it must be remembered that the cause of weight gain is not the hormone
insulin as protein proponents claim, but rather the portion size of the
diet that has, and still is, being recommended as nutritionally sound.
Protein and fat are needed daily as sources of fuel for the body, but what
needs to be decreased in our diet is overall calorie intake. In addition,
the other vital component to achieve weight loss is exercise. Our environment
today makes it very convenient to lead sedentary lives. Study after study
has confirmed that the key to losing weight and keeping it off is to exercise
regularly and eat a low-calorie, low-fat diet that is mostly composed of
complex carbohydrates (Alberts, 1997). Americans must realize there is
not a quick fix that will lead to long lasting weight changes. Until we
pay more attention to the amount we are eating as opposed to looking for
loopholes in our dietary composition, the increasing weight trend that
is sweeping our country will persist.
Alberts, N., "Protein versus carbs: getting the balance right," Self, March 1997, 130-133.
Atkins, R.C. Dr. Atkins' New Diet Revolution. New York: M. Evans & Company, Inc., 1992.
Bates, C.D., "Protein Propaganda," Shape, April 1997, 134-139.
Bogardus, C., Lillioja, S., Mott, D.M., Hollenbeck, C., and Reaven, G. 1985. Relationship betweeen degree of obesity and in vivo insulin action in man. Am. J. Physio, 248: E286-E291.
Brownell, K.D., Steen, S.N. 1987. Modern Methods for Weight Control: The Physiology and Psychology of Dieting. The Physician and Sports Medicine, 15(12): 122-137.
Cooney, G.J., Storlien, L.H. 1994. Insulin action, thermogenesis and obesity. Billiere's Clinical Endocrinology and Metabolism, 8(3): 481-502.
Eades, M.R., Eades, M.D. Protein Power. New York: Bantam Books, 1996.
Lissner, L., Steen, S.N., Brownell, K.D. 1992. Weight Reduction Diets and Health Promotion. Am J Prev Med, 8: 154-158.
Kirby, J. "Diet Smart: Carbs vs. Protein," Fitness, January/February 1997, 64-69.
Sears, B. 1995. The Zone. New York: Harper Collins, 1995.
Sharma, A.M. 1992. Effects of Nonpharmacological Intervention on Insulin Sensitivity. Journal of Cardiovascular Pharmacology, 20(11): S27-S34.
Vazquez, J.A., Kazi, U. and Madani, N. 1995. Protein metabolism during
weight reduction with very-low-energy diets: evaluation of the independent
effects of protein and carbohydrate on protein sparing. Am J Clin Nutr,
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