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1 From the Center for Human Nutrition, University of Colorado at Denver and Health Sciences Center, Denver, CO
2 Address reprint requests to JO Hill, Center for Human Nutrition, University of Colorado at Denver and Health Sciences Center, Ninth Avenue, C263, Denver, CO 80262. E-mail: james.hill{at}uchsc.edu.
See corresponding article on page 1298.
Those trying to lose weight are quick to embrace the latest popular diet but are almost as quick to abandon it. This observation is evidenced by the rise and the apparent recent decline in the popularity of low-carbohydrate, high-fat diets in the United States. It is interesting that the public seems ready to abandon these diets, despite evidence of their effectiveness. Several randomized controlled studies have shown that these diets are effective in producing weight loss and metabolic improvements over 6 mo in obese patients (1-5). The problem seems to be that the greater weight loss achieved with these diets is not maintained over time (1, 5). It is not clear whether this is due to the waning effectiveness of the diet or to the inability of most people to maintain this diet.
If history is any indication, the public is now looking for the next popular weight-loss diet. Most weight-loss diets are based on a particular macronutrient composition, and the potential combinations are limited. Because low-fat and low-carbohydrate diets have already been popular choices, one good possibility is that a high-protein diet will be the next popular diet (6). If high-protein diets do become the "next big thing," it would be useful to scientifically evaluate the safety and efficacy of these diets to determine whether they represent another passing fad or whether they can be a useful tool for weight management.
In this issue of the Journal, Noakes et al (7) report the results of a 12-wk study that evaluated high-protein (HP) diets intended for weight loss. They randomly assigned overweight and obese patients to 2 different hypocaloric diets. Both diets were low in fat, but one (HP diet) was higher in protein (34% compared with 17%) and lower in carbohydrate (46% compared with 64%) than the other, which was high in carbohydrate (HC diet). Two important messages emerged from this study. First, Noakes et al found that the hypocaloric HP diet produced weight loss comparable to that of the HC diet and provided nutritional and metabolic benefits that were equal to or in some cases greater than those seen with the HC diet. Second, in a post hoc analysis, they found that obese subjects in the top 50% of blood triacylglycerol concentrations at baseline lost more weight with the hypocaloric HP diet than with the hypocaloric HC diet. Thus, the study is noteworthy in that it suggests that high-protein diets are effective at both producing weight loss and improving risk factors for diabetes and heart disease and that it may be possible to identify persons who do particularly well with high-protein diets.
The first message from this study is important but should be interpreted with caution. Many different types of diets can produce substantial weight loss in the short term. Most obese persons attempting to lose weight do not fail in losing the weight but rather fail in maintaining the weight loss. We need to know whether high-protein diets are just alternative ways for some people to achieve weight loss (and probably gain it back) or whether they may be useful over the long term. We need research studies to answer at least 2 important questions: 1) Can high-protein diets be maintained permanently? and 2) Can high-protein diets help persons to permanently maintain their weight loss and the metabolic improvements they achieve? Answering these questions will require studies that focus not just on weight loss but on the long-term maintenance of weight loss. These studies will be difficult and expensive to conduct; however, without them we cannot provide the best advice on which diet is best for weight maintenance and whether the best diet for weight-loss maintenance varies from person to person.
The second message from the study of Noakes et al is that it may be possible to identify patients who will respond particularly well to high-protein diets. It is logical and intriguing to think that we can maximize weight loss by matching patient to diet, even though we have little past success in doing so. Noakes et al speculate that the reason why their subjects with high triacylglycerol concentrations responded better to the HP diet was because they were insulin resistant and that insulin-resistant patients may do better with HP diets. Although this is an intriguing hypothesis, other measures of insulin resistance apparently do not predict success in weight loss. Furthermore, whereas triacylglycerol concentrations improved more with the HP diet, other factors associated with insulin resistance (glucose, insulin, and HDL cholesterol) did not. It is important not only that we develop a way of predicting who will respond to different diets but also that we understand why the responses are different. If we understand the mechanisms involved, we may be more likely to apply this information to individualizing diet for weight management. For example, insulin resistance may be the reason that some patients do better with high-protein diets, and it is known that people become more insulin sensitive with weight loss. Thus, the best diet for maintaining weight loss may be different from the best diet for achieving weight loss. It is also important to evaluate whether matching patient to diet will not only help maximize weight loss during the consumption of hypocaloric diets but will also help maintain weight loss.
It may be useful to consider weight management as consisting of 2 different phases: achieving weight loss and maintaining weight loss. The strategies that work for losing weight may not be effective for keeping weight off. We have found this to be the case in a review of the National Weight Control Registry, which follows 5000 people who have succeeded in maintaining weight loss in the long term (8). When it comes to choosing a hypocaloric diet, one size may not fit all. However, keeping weight off requires the achievement of a permanent balance between energy intake and energy expenditure. Here is where physical activity becomes critically important (8) and may even be more important than diet composition.
The question remains as to whether high-protein diets are a temporary tool for helping some people maximize weight loss or whether they represent a reasonable way for some people to eat permanently? The study by Noakes et al is a good start in addressing this question, but we must invest in long-term research studies to obtain a definitive answer.
ACKNOWLEDGMENTS
The author had no conflict of interest in regard to this editorial.
REFERENCES
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