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Dietary Protein and Weight Loss

Deciphering the science behind high-protein/low-carbohydrate diets.

When it comes to weight loss
these days, protein is the big nutrition buzzword. You’ve
probably been asked about at
least one of the several high-protein/low-carbohydrate (HPLC) diets in the last 2 years. The hype over them grows whenever someone announces that his weight loss was due to his eating whatever he wanted as long as fruits, vegetables, grains and many dairy products were not included.

Introduced in 1972 by Robert Atkins, MD, the HPLC diet achieved considerable popularity as a way to drop as many as 10 pounds in 1 week by replacing carbohydrates with protein and fat. However, people initially failed to attain the weight loss that it promised, and its popularity declined until the 1990s, when a wave of HPLC books—including Barry Sears’ The Zone: A Dietary Road Map, Atkins’ Dr. Atkins’ New Diet Revolution and H. Leighton Steward’s Sugar Busters! Cut Sugar to Trim Fat—emerged. The resurgence of HPLC diets has attracted not only average Americans but also athletes of all ages and levels trying to maximize both their weight loss and their performance.

Holes in HPLC Theory?

As mentioned, HPLC diets promote protein and fat consumption while eliminating most of the foods in three food groups (fruits, vegetables and grains) and some in the fourth (dairy products). If you’re like me, you intuitively know that, despite the considerable weight loss due to this approach, something is nutritionally fishy about it, yet HPLC diets have piqued the interest of the American public.

No one in the scientific community debates that HPLC diets definitely result in weight loss. The question is whether the weight loss is due directly to the protein in these diets or to universal facts regarding physiology and dieting in general. Researchers have found conflicting answers. Consider the three underlying claims made by proponents of HPLC diets.

Claim #1:
Weight Loss Is Due Directly
to High-Protein Intake

Advocates of HPLC diets maintain that maximizing protein consumption while minimizing carbohydrate consumption is the key to losing weight, but the fact is that HPLC diets are low in total calories. It is well accepted that, regardless of dietary composition, achieving negative energy balance—
by decreasing energy (calorie) consumption, increasing energy expenditure (exercising) or some combination of the two—is essential for weight loss. According to Atkins’ diet, during the first 2 weeks of the regimen, men should consume only 1,400 calories per day, and women should consume only 1,200 calories per day (Boucher 1999).

Claim #2:
Insulin Promotes Fat Storage

According to HPLC supporters, a high insulin level, caused by excessive carbohydrate consumption, is responsible
for weight gain. Insulin, an anabolic hormone released after eating, functions as the “key” for transferring glucose out of the bloodstream and into cells, where it is used for energy, growth and glycogen production. Higher insulin levels not only make available more glucose than cells can use but also increase
the level of lipoprotein lipase, the fat storage enzyme. Consequently, higher insulin levels are associated with increased fat deposition.

However, other research has shown that insulin can’t be blamed for causing obesity. If anything, obesity hinders the liver’s ability to clear insulin from the bloodstream, raising one’s insulin level to cause insulin insensitivity. Apparently, overweight and obese individuals mostly have this problem; most normal-weight people clear insulin from their bloodstreams easily.

To assess the effect of insulin level
on weight loss or fat loss, Golay et al. (1996a) and Golay et al. (1996b) fed different groups of subjects low-calorie diets. Carbohydrates constituted 15 percent, 25 percent or 45 percent of each group’s total calories respectively, and fasting insulin levels were much lower in subjects who consumed the lower-carbohydrate diets. Nonetheless, no difference in total weight loss or body fat loss was observed among the groups. If insulin caused weight gain, the group with the greatest decrease in insulin levels should also have experienced the greatest fat and weight loss.

Claim #3:
Weight Lost on HPLC Diets Is Fat

Promoters of HPLC diets claim that all of the weight that they lose is fat. However, research suggests that water loss is responsible for much of the rapid weight loss experienced on low-carbohydrate diets.

People who eat carbohydrate-rich foods on a regular basis store 400 to 500 grams of glycogen (carbohydrate), which contain 1,600 to 1,800 calories, so, theoretically, avoiding carbohydrates would deplete those glycogen stores quickly. The body stores 2.7 to 3.8 grams of water per gram of glycogen stored, so depletion of glycogen would mean an additional loss of the 2 to 4 pounds of body water stored along with it. Limiting carbohydrate intake limits glycogen formation (Ivy et al. 1988). Consequently, that water leaves the body.

Furthermore, water loss is known to coincide with sodium excretion (Capani et al. 1981). Research has found much more pronounced sodium excretion with HPLC diets than with high-
carbohydrate diets.

Research Revisited

The escalating rates of obesity in the U.S. have spurred further research efforts to understand HPLC diets. At the American Dietetic Association’s 85th annual meeting in 2002, in a lecture entitled “Emerging Health Benefits of Dietary Protein and Its Role in Weight Management,” David Layman, professor of nutrition in the division of nutritional sciences at the University of Illinois, Urbana-Champaign, presented the results of a study that he conducted to evaluate the efficacy of an HPLC diet on weight loss.

Study: Layman, D.K., et al. 2000. Carbohydrates vs. protein in diets for midlife women. FASEB Journal, 14, A564.

Subjects: The study subjects were 24 adult women ages 45 to 56 with body mass indices between 26 and 36. To be selected, all of them had to consume 55 percent of their total daily calories from carbohydrates, 15 percent from protein and 30 percent from fat (55/15/30) before the study.

Methods: The women were divided into two groups of 12. One group continued to eat a 55/15/30 diet; the other group ate a 40/30/30 diet. Both groups consumed 1,800 calories daily.

Results: After the first 4 weeks on the dietary protocol, the 40/30/30 group had lost an average of 3.73 kilograms (approximately 8.2 pounds), 3.05 kg (6.71 pounds) of which were fat and 0.68 kg (1.49 pounds) of which was a combination of water and muscle mass. No results were published for the women on the higher-carbohydrate diet.

Conclusions: HPLC diets definitely appear to aid weight loss, but few data illuminate whether weight loss on these diets is maintained better than or as well as weight loss on other, more balanced diets. Layman does conclude that HPLC diets offer greater satiety. This may be the most meaningful information yet.

According to Richard Mattes, PhD, MPH, RD, professor of foods and nutrition at Purdue University, eating protein helps one feel full sooner and on fewer calories than does eating carbohydrates or fat. Especially for clients who have poor appetite management or insist that they never feel full, this fact may support following a higher-protein diet. Although no concrete data currently exist to specify what types of protein (soy, whey or meat) promote fullness soonest or most efficiently, solid protein sources apparently provide greater satiety than do liquid protein sources.

Advice to Clients

Protein will remain in the nutritional spotlight for quite some time. For now, advise clients concerned about weight loss to consume an adequate amount
of protein, according to their goal weight. Use the new Dietary Reference Intakes of 10 to 30 percent of their total daily calories.

In addition to protein, it is important to stress “quality calories” to clients by encouraging consumption of fruits, vegetables and whole grains for nutrients and fiber. Like protein, fiber is known to help people feel full. Foods such as fruits, vegetables and soups also contain a considerable amount of water, which makes them denser than other foods to promote a feeling of fullness as well. Moreover, eating whole, fresh fruits and vegetables simply slows down chewing and digestion to decrease the total number of calories consumed.

Because calorie guidelines are somewhat arbitrary, I recommend calorie amounts both that seem reasonable to produce a weight loss of 1 to 2 pounds per week and that my clients feel they can adopt most days of the week. For example, if I suggest a 2,000-calorie diet, I recommend that 30 percent of those calories come from protein (600 calories, or 150 grams of protein). If that protein intake is well tolerated, I suggest that the client maintain it for several weeks and see how he does.

If the client finds eating 150 grams of protein every day too monotonous, he may reduce his protein consumption and boost his carbohydrate consumption. Your ultimate goal is to help clients understand that weight management is about not only weight loss but also behavior modification.


Boucher, J. 1999. News you can use: The high-protein, low-carbohydrate diet craze. Diabetes Care and Education, 20 (5), 26-30.
Capani, F., et al. 1981. Modifications of the water balance and urinary excretion of sodium and potassium in obese subjects on a “single-meal” low-calorie diet. Bollettino della Societa Italiana di Biologia Sperimentale, 57 (3), 316-9.
Gabel, K.A., & Lund, R.J. 2002. Weight loss at a cost: Implications of high-protein, low-carbohydrate diets. Journal of Physical Education, Recreation & Dance, 73 (2), 18-21.
Golay, A., et al. 1996a. Similar weight loss with low- or high-carbohydrate diets. American Journal of Clinical Nutrition, 63 (2), 174-8.
Golay, A., et al. 1996b. Weight-loss with low or high carbohydrate diet? International Journal of Obesity and Related Metabolic Disorders, 20 (12), 1067-72.
Ivy, J.L., et al. 1988. Muscle glycogen synthesis after exercise: Effect of time of carbohydrate ingestion. Journal of Applied Physiology, 64 (4), 1480-5.
Layman, D.K., et al. 2000. Carbohydrates vs. protein in diets for midlife women. FASEB Journal, 14, A564.
Long, S.J., Jeffcoat, A.R., & Millward, D.J. 2000. Effect of habitual dietary-protein intake on appetite


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