Although there is public awareness about the problem of obesity in the United States, the prevalence of obesity continues to rise. Due to this problem, fad diets abound. Since there does not seem to be scientific unity on what is the largest nutritional cause of obesity, non-scientific prescriptions for weight loss have flourished. Many have focused on dietary protein, dietary fat, dietary sugar, or overall calorie control. The purported benefits of such diets include weight loss, reduced hunger, even prevention of chronic disease. In this review, many of today’s fad diets will be examined to determine whether there is scientific research behind them, and what the research suggests regarding their effectiveness.
Steven Jonas, M.D., M.P.H., suggests that a reduction in caloric intake is best achieved by substituting fattening foods for healthy carbohydrates: grains, fruit, and vegetables, without overdoing total calories for the day. He also suggests that most of the “anti-carb” stuff you hear these days is meaningless. Carbs by themselves do not lead to weight gain (any more than fats eaten in small enough quantities do). Too much of any kind of carbs, but especially the “wrong carbs,” will lead to weight gain (4).
So, then, why don’t more prospective weight-losers follow that pathway? That is because, as most everyone reading this article knows, healthy eating is easier said than done. If there is a quick-fix or easier alternative to be tried, then most humans will give it a go.
Intuitively fad diets do not make sense, says Jonas. Eating only one kind of food or eating your food in a particular pattern is not sound nutritionally (4). The main attraction of these diets is that they come with some version of “lose ten pounds in seven days,” or “forty pounds in eight weeks.” Second, they are always described as “easy” and requiring “no will-power.” Third, they invariably tell the dieter exactly what to eat. No choices will need to be made. Finally, if exercise is ever addressed, it is mentioned in passing, as an afterthought. These authors make the whole approach sound easy.
Perhaps the most popular weight-loss diets in America are the low-carbohydrate diets. Recently, several best-sellers such as Dr. Atkins' New Diet Revolution, Protein Power, and Sugar Busters have promoted the effectiveness of very low-carbohydrate diets (high-fat and high-protein diets). But are these diets safe? These diets could be described as “ketogenic” because of the metabolic shift from deriving energy primarily from carbohydrates to ketones, a fat byproduct produced when carbohydrates are not readily available for extended periods of time (2). The problem is that the abundance of books and magazine articles promoting low-carbohydrate diets are often deficient of science. Many lack appropriate research, such as inappropriate exploration from animal studies (2).
The attraction to these sorts of diets is that dieters can lose weight while eating as much protein and fat as they like. This claim, however, is based on research evidence that individuals on a diet restricted in carbohydrate, but unlimited in fat and protein tend to automatically restrict their calories (2). Analysis of the nutrient content of several low-carbohydrate diets revealed them to be low-calorie diets, with most providing around 1,000-1,200 calories (2). So is the claim that dieters can lose weight while eating unlimited amounts of food false? Science suggests that body-fat loss requires some type of shift in energy balance that leads to either increased caloric expenditure or decreased calorie intake (2).
However, these diets are also popular due to the satiety (reduced hunger) factor. Satiation informs you to stop eating, and satiety signals you to not start eating again. Of all the energy-yielding nutrients, protein is the most satiating (2). Therefore, the high-protein approach is appealing because of the satiety it imparts.
The Atkins Diet
There were four studies that examined the efficacy of the low-carbohydrate diet on weight loss and reduction of cardiovascular risk factors. In each of the three randomized controlled trials, dropout was significant, but was less for the Atkins than for the low-fat groups (6). Although the low-carbohydrate diet produced greater weight loss for up to six months, this weight loss was not maintained at a one-year follow-up. However, significant improvements were shown in high-density lipoprotein cholesterol (HDL), insulin sensitivity and triglycerides (6). Another study suggested that high-protein meals may have particularly beneficial effects on energy expenditure and fat oxidation in overweight subjects (1).
Concerns continue though about the long-term safety of these sorts of diets. Diets consisting of large amounts of animal protein, saturated fat, and cholesterol are associated with cardiovascular disease, cancer, and other chronic illnesses (6). High-protein diets are also associated with calcium loss and decreased urinary citrate (6).
In a comparison study between a low-carbohydrate Atkins-type diet with a moderate-carbohydrate, low-fat, high-fiber diet using a partial meal-replacement approach, both diets produced significant weight loss. However, the low-carbohydrate diet produced a greater decline in percentage body fat (6). The researchers concluded that the ability of the Atkins-type diet to produce weight loss has been attributed to the depletion of glycogen stores, the release of bound water, increased satiety due to ketogenesis and high protein content, and limited food choices (6).
The Sugar-Free Diet
The Sugar Buster's diet steers dieters away from refined sugars and other carbohydrates with a high-glycemic index. Foods with a high-glycemic index raise blood glucose levels quickly and foods with a low-glycemic index raise blood glucose levels much more slowly. The theory suggests that eating high-glycemic index foods cause a glucose spike, followed by a big drop in glucose levels that stimulate a craving for more high-glycemic index foods, which then results in obesity (3).
In this diet you consume 30% carbohydrates, 30% protein, and 40% fat. Along with most sugar, banned foods include white bread, pasta, white rice, potatoes, corn, beets, carrots, and bananas, (similar to Atkins). However, small portions of whole grains are permitted.
Daily caloric consumption amounts to about 1,200 calories, so dieters tend to lose weight because they’re eating fewer calories (3). The drawbacks are that this diet restricts many foods containing essential vitamins and minerals. Also many dieters are not likely to stick with a diet that permits very little sugar.
The Blood-Type Diet
Then you have the Eat Right for Your Type (ERFYT) diet, which is based on the theory that people should eat certain foods that are compatible with their blood type. The claim here is that when people with certain blood types consume some foods, substances from the food called lectins circulate in the blood stream and cause blood cells to agglutinate or clot. This clotting then supposedly causes other problems, such as liver and kidney troubles. The ERFYT diet is supposed to make the dieter healthier by eliminating lectins, but the research is unsubstantiated (3). Again, it’s because fewer calories are being consumed.
What is most interesting is that since Type O blood-type individuals are recommended to eat a high-protein, low-carbohydrate diet, they are the ones who seem to lose weight with this diet (3).
The Zone Diet
The Zone diet recommends eating 40% carbohydrates, 30% protein and 30% fat. Once again, if this diet works, it’s potentially due to being low in calories, ranging from 1,000 to 1,600. This lower carbohydrate diet may also put the body in to ketosis, and no scientific research supports this diet either (3).
The South Beach Diet
The South Beach diet is a high-protein, low-fat, low-carbohydrate plan that focuses on low glycemic-index foods. The diet has three phases: initial rapid weight loss, gradual weight loss, and maintenance. In contrast to the Atkins diet, the South Beach diet does not severely limit carbohydrate intake. It also does not promote fat intake. It focuses on “good carbs” such as fruits, vegetables, whole grains, and “good fats,” which are unsaturated and low on the glycemic index (8).
Inconsistencies abound in this book. The book says that the diet is “distinguished by the absence of calorie counts … or even rules about portion size” and that you should not “even think about limiting the amount you eat,” but then proceeds to count calories and measure out servings every step of the way (5). Another problem is that the diet claims that it “has been scientifically studied” and “proven effective,” but not a single reference to a scientific journal is made (5). Nevertheless, weight loss will occur, but not due to blood sugar levels as they would like you to believe. Weight loss occurs due to consuming somewhere around 1,500 calories per day (5).
The Paleolithic Diet
The Paleolithic diet (the diet that humans are supposed to have eaten during 2 million years as hunger-gatherers) includes meat, seafood, fish, fruit, vegetables, root vegetables, and nuts (2). No refined foods including sugar are to be consumed in this diet. It is not primarily a weight-reduction diet, but may provide high satiety at a low energy intake, and could contribute to weight control or weight loss. This diet also claims to prevent many diseases such as cancer and heart disease. However, there have been no intervention studies to support the claimed effects of such a diet (2).
Commercial Diet Plans
Beyond the low-sugar, low-carbohydrate sphere of dieting books, there are also the tried-and-true commercial diets such as Weight Watchers, Jenny Craig, LA Weight Loss, Medifast, and eDiets. These all suggest a low-calorie diet plan. One study reported that those who regularly attended Weight Watchers, which features an exchange diet, lost approximately 5% of their initial weight over a three-to-six-month period (8). The Jenny Craig diet plan features prepackaged meals, and Medifast’s diet is provided through meal replacement. Most others involve individual meal preparation.
The Ornish Diet
The Ornish diet is based on a food intake that is 10% fat, 20% protein, and 70% carbohydrates. The few plant-based foods that are excluded, including all oils (other than 3 grams/day of flaxseed oil or fish oil to provide additional omega-3 fatty acids), nuts, and avocados. The diet consists primarily of fruits, vegetables, grains, and beans, including soy-based foods, supplemented by moderate amounts of nonfat dairy and egg whites (8). There are no caloric restrictions as long as the diet is in the confines of the recommended foods.
Conclusions
A study was done which compared the Atkins, Ornish, Weight Watchers, and Zone diets for how effective they were for weight loss and reducing heart-disease risk. Patients were randomized to one of the four diets, received counseling for two months, and then had to follow the diet on their own for ten months. At the end of one year, all patients lost weight – approximately four percent. All groups showed a reduction in LDL cholesterol and an increase in HDL cholesterol levels. On the negative side of the equation, however, was the fact that half of the patients enrolled in the Atkins and Ornish programs had dropped out, and a third of patients in the Weight Watchers and Zone program had quit (8).
Does fat restriction affect the composition of weight loss? There is some indication that more weight loss is seen with a diet higher in protein or lower in carbohydrate (7). In support of higher protein intake, fat loss was greater after six months of a high-protein versus a high-carbohydrate diet (both diets were equal in fat). Higher protein intake is also shown to result in better weight maintenance, as long as the dieter sticks to the plan (7). In many clinical trials, adverse effects of very-low-carb plans have not been observed. However, individuals with a history of gout or renal issues are advised not to follow such a plan (7).
It must be understood that the similarity between most fad diets is the fact that there is calorie reduction. Also, dieters probably become better educated regarding food and the ability to read a nutrition label. While any diet can work if you follow it correctly, there is also the potential for negative behaviors, such as the thought that there is only one possible solution to weight loss, or the lack of nutrition one may receive from eliminating a particular food group.
It is safe to say that Americans eat too many calories in the way of refined or processed (as opposed to whole-wheat) carbohydrates, which means too much cake, candy, pastries, muffins, ice-cream, pasta, outsized bagels, soda pop, white bread, pizza, sweetened cereal, and French fries. The servings are inappropriately large (and frequent), which is definitely contributing to our expanding girth. However, we do not need a 300-page diet book to advise us on making adjustments. We need to eat smaller portions less often, and cut out the junk! Exclusion-type diets may provide weight loss in the short term, but are difficult to maintain over the long haul. There is also a risk of deficiency of certain vitamins and minerals. Although fad diets are generally not recommended for the long term, it is imperative to decide what one can stick with as a lifestyle choice. If you cannot bear the thought of never eating a slice of bread again (even though research suggests that you will lose weight with a low-carb diet), then a high-protein diet is not for you. The moment a diet plan is broken, is the moment the pounds will begin creeping back on.
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