Although the number of people dieting continues to increase, the rate of obesity also continues to increase. The latest solution is the high-protein (or, more accurately, high-fat), low-carbohydrate diet. People lose weight while following this diet, but there is no evidence that the weight lost is maintained over the long term. In addition, the diet eliminates whole categories of foods known to have health benefits—fruits, whole-grains, vegetables, and milk. Energy restriction, not manipulation of macronutrients, is associated with weight reduction in the short term. Because we do not yet know how to maintain weight loss over the long-term, diabetes care providers should advise patients to eat healthfully, be physically active, and keep food and blood glucose records.
The rate of obesity and the number of “dieters” are increasing in parallel! Surveys consistently show that most adults are trying to lose or maintain weight.1 More than 54 million Americans are currently on a diet,2 yet the prevalence of overweight and obesity continues to increase. If dieting worked, obesity should be decreasing or at least not increasing. It is true that many dieters succeed in taking weight off, but very few—maybe just 5%, but at most 10%—manage to keep the weight off over the long term.3–5
Statistics suggest that about half of the adult population in the United States is overweight (body mass index [BMI = weight/height2] 25–30), and 16% are obese (BMI >30).6 It is not surprising that so many consumers are searching for the “magic bullet” that will allow them to lose weight quickly and effortlessly. Unfortunately, health professionals also contribute to this phenomenon by constantly warning the public and their patients about the perils of being overweight. And herein lies the quandary—how to solve the problem of increasing obesity and its related health risks without making the problem worse.
Many Professionals Claim to Have the Solution to Weight Loss
There seem to be many “authorities” out there who have the answer—buy their book, buy their product, come to their program, and you will lose weight. A search of Amazon.com using the words “weight loss” revealed 1,214 matches with 58% published after 1999 and 85% since 1997.5 Many of the 20 best sellers at Amazon.com promote some form of carbohydrate restriction—Dr. Atkins’ New Diet Revolution, The Carbohydrate Addict’s Diet, Protein Power, Lauri’s Low-Carb Cookbook. So people do buy their books and products and attend their programs and do lose weight.
But although there appear to be easy solutions to the weight-loss problem, these solutions tend to be, at best, temporary. Even the “gold standard” behavioral weight-loss programs—those involving 16–24 treatment sessions over 6 months including self-monitoring, low-fat diet, and exercise—consider an average weight loss of 18–20 lb a success, but also report that participants retain only 60% of their initial weight loss 1 year after treatment.3 Another study4 reported the average duration of weight-loss programs to be 18 weeks, with moderately obese individuals losing 10% of their body weight. However, at 1 year, 34% had regained the lost weight, and at 3- to 5-year follow-up, there was a gradual return to baseline weight.
To determine what is required to maintain weight loss, a national registry searched nationwide and found a small number (in comparison to the number of people who diet) of successful weight losers. In a descriptive study of 784 participants,7 the investigators reported that participants who lost an average of 66 lb (30 kg) and kept off at least 30 lb (13.6 kg) for an average of 5.5 years expend an average of 2,800 kcal per week through physical activity or an average of 1.5 h of exercise daily and eat less than 1,400–1,500 kcal with ∼20% of their calories from fat. In other words, their life is devoted to weight loss! But we all want an easier answer, so the parade of quick fixes continues.
Given the beneficial effects of weight-loss treatments on medical conditions such as type 2 diabetes and cardiovascular disease, reputable researchers continue to search for innovative ways to improve treatment outcomes.8 As researchers continue to search for solutions to the problem of weight regain after weight loss, other medical professionals “buy into” the claims made for the high-protein, low-carbohydrate diets, and without any research documenting the long-term effectiveness of this solution, they recommend the latest book to their patients.
The Latest Solution: High-Protein, Low-Carbohydrate Diets
The current diet fad promises results with a high-protein, low-carbohydrate diet (which in actuality is a high-fat, low-carbohydrate diet). With only three macronutrients—carbohydrate, protein, and fat—to manipulate for changes in energy intake, there are not many options left to sell a new diet book. We have gone through the high-carbohydrate phase—bagels, pretzels, and low-fat cookies. It is unlikely that the current fad diet will be blatantly promoted as a high-fat diet—everyone has heard about the perils of eating fat. So, we are left with recycling the concept of a high-protein diet.
High-protein, low-carbohydrate diets claim to promote weight loss and improve blood glucose control. And while such diets are followed, they usually do both. Weight loss and improved glucose control are both important goals for people with type 2 diabetes, so why not recommend such diets to all persons with type 2 diabetes?
Advantage Claims for High-Protein, Low-Carbohydrate Diets
The advantages of the high-protein, low-carbohydrate approach are that diets that eliminate a whole category of nutrients—in this case, carbohydrate—are lower in calories and thus result in weight loss. With a high-protein intake and strict limitation of carbohydrate, water stored with glycogen (carbohydrate) is released. This rapid loss of fluid is an initial boon to dieters looking for fast results.
Fasting ketosis, which results in loss of appetite, may also develop. Furthermore, few people can eat endless amounts of animal protein and fat for weeks on end, and so they eat less and less. The good news is that with a high-protein diet, weight is lost, insulin needs drop, and blood glucose and sometimes even lipid levels improve. It works, at least temporarily.
Although the authors of the popular books all take a slightly different approach, the basic premises are fairly similar. Eating a high-carbohydrate diet, they claim, makes people “fat” because carbohydrate increases blood glucose levels, causing a greater release of insulin, and higher insulin levels cause carbohydrate to be stored easily as fat (in adipose cells). Eating a high-protein diet, the argument goes, leads to weight loss, decreased insulin levels, and improved glycemia. However, neither this nor the claim to “cure” insulin resistance—the oversecretion of insulin that proponents of these diets say causes the lipogenesis—with a low-carbohydrate, high-protein diet is supported by scientific evidence.
Nor is there good evidence that insulin resistance from eating a diet rich in starchy foods and sugar is the cause of obesity. It is more likely the other way around—it is obesity that is associated with insulin resistance. Increased physical activity, energy restriction, and/or moderate weight loss have been shown to improve insulin sensitivity—not changes in the protein-to-carbohydrate ratio.9–11 A high fat intake, regardless of the type of fat (saturated, polyunsaturated, or monounsaturated) has also been linked to insulin resistance,10,12–15 so reducing fat intake may also help.
High-protein diets claim to offer other benefits. For example, protein stimulates the release of glucagon, a hormone that raises the level of blood glucose and counteracts the action of insulin; so eating right means balancing insulin and glucagon levels. Therefore, the argument goes, if you don’t eat enough protein, your body releases too much insulin and not enough glucagon. It is true that the balance of insulin and glucagon release is important in the metabolism and storage of nutrients. But it is doubtful that you can change the balance by eating more protein.
Another claim is that, if the right kinds of fat are eaten, individuals will not become fat. However, there appears to be a hierarchy for the autoregulation of substrate utilization and storage that is determined by storage capacity and specific fuel needs of certain tissues.16 Alcohol has the highest priority for oxidation because there is no body storage pool for it, and conversion of alcohol to fat is energetically expensive. Amino acids and carbohydrates are next in the oxidative hierarchy. Body proteins are functional, and there are no storage depots for amino acids. There is also a limited capacity to store carbohydrate as glycogen, and conversion of carbohydrate to fat is energetically expensive, as well. In contrast, there is virtually unlimited storage capacity for fat, largely in adipose tissue, and the storage efficiency of fat is high.
Because of the oxidative priority of alcohol and protein, the body has an exceptional ability to maintain their balance across a wide range of intakes of each. Carbohydrate oxidation closely matches carbohydrate intake.17,18 Therefore, the amount of fat oxidized or stored is the difference between total energy needs and the oxidation of the other priority fuels—alcohol, protein, and carbohydrate.
Proponents of these diets also claim that more protein in the diet increases the satiety value of the meal, leading people to eat less. Although the effects of dietary fat and carbohydrate on regulation of energy intake, weight loss, and satiety have been studied, only limited research has been conducted related to protein. Short-term studies have suggested that protein per calorie exerts a more positive effect on satiety than both carbohydrate and fat.19–21 However, this may not translate into eating fewer calories. Stubbs et al.,21 in a 1-day study, reported that although subjective hunger was less after a high-protein breakfast compared to a high-fat or high-carbohydrate breakfast, lunchtime intake 5 h later and energy intake for the rest of the day were similar after all three breakfasts.
Skov et al.22 studied the effect on weight loss in obese subjects by replacement of carbohydrate with protein in ad libitum fat-reduced diets. All foods were supplied to the 50 subjects for 6 months and could be consumed ad libitum. Subjects were randomly assigned to either a high-protein (25% protein, 45% carbohydrate) or high-carbohydrate (12% protein, 58% carbohydrate) diet. Both diets were low in fat (30% of energy). At 6 months, the high-protein group had lost an average 8.9 kg (20 lb) with a fat loss of 7.6 kg (17 lb), compared with the high-carbohydrate group average loss of 5.1 kg (11 lb) with a fat loss of 4.3 kg (9 lb).
Over the course of the study, energy intake was lower in the high-protein group by ∼8,000 calories (∼42 kcal/day), which probably accounted for the difference in weight loss. The researchers attributed the decrease in calories to the higher satiating effect of protein compared with carbohydrate. The real test of effectiveness would be to follow these subjects for the next 2 years to identify food choices after the completion of the study and to determine whether weight lost during the study was maintained.
Disadvantages of High-Protein, Low-Carbohydrate Diets
Aside from the problem that no long-term research is available to document that high-protein, low-carbohydrate diets maintain weight loss any better than traditional weight loss diets,3–5 what are other concerns posed by these diets?
A major concern is that foods with proven health benefits are eliminated. There are health needs for the nutrients found in grains, fruits, vegetables, milk, and other carbohydrate-containing foods.23–27 When analyzed,5 these diets are low in calories—e.g., 1,152–1,627 kcal/day. However, they are also high in fat (55–60%), especially saturated fat; cholesterol; and protein (25–30%), mainly animal. The excess protein also has the potential to cause the body to lose what little calcium is ingested. They provide lower than recommended in-takes of vitamin E, vitamin A, thiamin, vitamin B6, folate, calcium, magnesium, iron, potassium, and dietary fiber, which can contribute to constipation. Taking a supplement to replace missing nutrients is not the complete solution either, because all of the essential nutrients found in foods have not yet been identified and so cannot be replaced.
The long-term effect on lipids from these diets is unknown. A study of subjects following a high-protein, low-carbohydrate diet for 12 weeks reported substantial increases in plasma levels of both uric acid and LDL cholesterol, decreases in triglycerides, but no increase in HDL cholesterol levels, despite effective weight loss.28
We are reminded that popularity is not credibility. There is little research published in peer-reviewed journals to support low-carbohydrate, high-protein diets. High-protein diet books are based on personal experiences and testimonials and contain theories that usually would not survive peer review. Authors quote their own studies as proof of their diet’s effectiveness. However, even their own studies have not shown this to be an approach that individuals can follow over the long term. Long-term studies are necessary to determine how long individuals can comfortably consume a high-protein diet in the real world.
The bottom line: people are obese not because they eat too much carbohydrate, but because they eat too many calories. Eating carbohydrate does not make people fat unless they overeat on carbohydrate (just as it would to overeat on protein or fat). There is evidence that high levels of dietary fat are associated with high levels of obesity,29 but there is no evidence that high intake of “simple” sugars or carbohydrate causes obesity, hyperglycemia, or insulin resistance without dietary fat.30
Furthermore, should medical professionals be recommending a diet known to be nutritionally inadequate to people with diabetes in an effort to improve blood glucose control? This is an ethical question that deserves an answer.
Does Habitually Following a Low-Carbohydrate Diet Correlate With Lower Weight?
The U.S. Department of Agriculture initiated a research program to assess the relationship between prototype popular diets and diet quality, food consumption patterns, and BMI.31 To do this, researchers analyzed the food intake of 9,372 adults from the 1994–1996 Continuing Survey of Food Intake by Individuals. These data were used because they illustrate what people in the United States are actually eating. Popular diets were divided into three categories that represent more than 90% of the popular diet books now on the market: 1) low-carbohydrate diets (defined as <30% of energy from carbohydrate); 2) moderate-fat, moderate-carbohydrate diets (30–55% of energy from carbohydrate); and 3) very-low-fat, high-carbohydrate diets (>55% of energy from carbohydrate).
The largest portion—64%—fell into the middle group. Energy intake, total fat, saturated fat, protein, and mean BMI for subjects consuming these diets are listed in Table 1. Diet quality was highest for the high-carbohydrate group; diets high in carbohydrate and low to moderate in fat also tended to be lower in energy. BMIs were significantly lower for the high-carbohydrate diets, and the highest BMIs were noted for those on a low-carbohydrate diet. Their conclusion: weight loss is independent of diet composition. Energy restriction, not manipulation of macronutrients, is associated with weight reduction in the short term.
Focus on Blood Glucose Control, Not Weight Loss
There may be better advice, but it isn’t very new or exciting. Moderation is generally the best approach—eating a healthful diet, being more physically active, and, if an individual has diabetes, keeping food records along with blood glucose records so that blood glucose levels can be kept under optimal control.
Perhaps we need to even ask why we have focused lifestyle changes for type 2 diabetes on weight loss instead of on improving blood glucose control. All of us would like to be able to help individuals lose and maintain weight loss, but research reveals little long-term success. Research is clarifying why weight loss is difficult32–34 and documenting the psychological problems associated with the dieting process.35 Obesity is associated with the development of chronic diseases, such as type 2 diabetes, and prevention of chronic diseases may require a better understanding of what controls appetite and better tools, including medications, to prevent weight gain or assist in weight loss. However, treatment for individuals who already have type 2 diabetes needs to focus on lifestyle strategies for the improvement of the associated metabolic abnormalities.
Early in the course of the disease when insulin resistance is present, energy restriction not related to weight loss and moderate weight loss (5–10% of body weight or 10–20 lb) have been shown to improve glycemia.36 But as the disease progresses and insulin deficiency becomes the central issue, it may be too late for weight loss to be helpful.37
Fitness, Not Thinness, Reduces the Risk of Mortality
Blair and associates38–40 evaluated the relationship between changes in physical fitness, obesity, and risk of mortality in ∼25,000 men. Baseline physical fitness and mortality during 8 years of follow-up within various BMI strata were reported.39 In all BMI categories, men who were fit had lower death rates compared with men with low fitness levels. Differences in mortality were not caused by differences in body weight but rather by differences in fitness.
In a follow-up study,40 the health consequences of body fatness and cardiorespiratory fitness in relation to all-cause and cardiovascular mortality were reported. The investigators found that obesity did not appear to increase mortality risk in fit men regardless of their BMI. Fit men had greater longevity than unfit men regardless of their body composition or risk factor status. In fact, obese fit men had a lower risk of all-cause and cardiovascular mortality than lean unfit men. Their conclusion: for long-term health benefits, we should focus on improving fitness by increasing physical activity rather than relying only on diet for weight control.
What Advice Should We Give to Individuals Who Struggle With Weight Issues?
The first message to give individuals with weight problems should be to eat healthfully. Today, we may not know how to help individuals maintain weight loss, but we do know what constitutes a healthy diet. Studies have documented the importance of foods containing carbohydrate—fruits, vegetables, whole grains, low-fat milk products—in a healthy lifestyle. However, it is true that carbohydrate foods containing large amount of sugars are not essential to good health—even if they are enjoyable. They should be eaten with caution. Low-fat diets have also been shown to contribute to weight maintenance.41–43
Encourage physical activity. Studies have also shown that individuals can become fit by accumulating only 30 min of physical activity throughout the day.44 Having a dog that requires walking several times a day can contribute not only to psychological well-being through the enjoyment of having a pet, but also to improved physical health.
If you think individuals with type 2 diabetes must lose weight, remember that all that is required is a 10-lb loss. The challenge for health professionals is to convince individuals that this should be their goal. Foster et al.45 reported that women participating in a weight-loss program expected to lose 34% of their body weight. However, after 48 weeks of treatment, they had lost only 16% of their initial weight, and they reported being unsatisfied with their weight loss.
Perhaps the most helpful thing we can do is to help individuals who struggle with their weight to “like themselves.” They are important people both for themselves and for those who they care about. Even if we can’t help them maintain weight loss, we can help them make changes for a healthier lifestyle, and we can help them manage their diabetes better.
Portions of this article originally appeared in:
Marion J. Franz, MS, RD, LD, CDE, is a nutrition/health consultant with Nutrition Concepts by Franz, Inc., in Minneapolis, Minn.
- American Diabetes Association