At NutritionalCenter.com, we receive hundreds of emails every week regarding diet and nutrition. Some of the most frequently asked questions deal with high-protein and fat diets that brand carbohydrates as "evil" and as the reason for the prevalence of obesity in our society today.
Such diets are not new. They have waxed and waned in popularity over the years, with the previous crescendo occurring in the '70s. The recent popularity most likely stems from the fact that, in spite of previous dietary recommendations and the prevalence of low-fat and non-fat foods, more and more of the population continues to reach obesity. This increase in obesity is because people are not following current diet and exercise recommendations. Let's examine how proponents or marketers of high protein diets trick their patrons. The following are the most prevalent claims made in support of these diets:
Claim 1. People are not getting fat from consuming too many calories, but from the consumption of carbohydrates, especially high glycemic index (GI) ones.
Despite the claims of these diets, obesity and weight gain are the result of positive energy balance.1,2 If one consumes more calories than they expend, then there will be an increase in mass. One's genetics and lifestyle determine how easy it is for this to occur.3 The problem is that society's caloric intake has increased (by about 300 calories in the last decade) and its caloric expenditure has decreased (due to technology and labor-saving devices).4,5
Glycemic index refers to the effect on the blood sugar (BS) level of equivalent amounts of CHO contained in different foods.6 In other words, how quickly BS rises and how much insulin is released in response to a particular food. GI measures a single food source eaten by itself and on an empty stomach. Several studies have shown that high GI foods do not have the same glycemic response when given as part of a mixed meal.7,8 Many, if not most, high GI foods eaten today are refined foods, high in added sugar, and would not be considered wise food choices by any standard.
We must still face the truth, which is that high GI foods, while possibly not the wisest use of calories, are not responsible for weight gain. People get fat when they consume too many calories in relation to expenditure.
Claim 2. Carbohydrates stimulate insulin release, causing the body to store fat. This accompanying insulin production causes insulin resistance (IR) and the development of obesity and NIDDM (type II diabetes).
It is interesting that none of these diet proponents mention that protein also stimulates insulin release.9 Other than genetic IR, most scientists acknowledge that it is obesity itself (due to an excessive energy intake) that leads to IR, not the other way around.2
Insulin resistance is often accompanied by several other conditions collectively known as "Syndrome X." Characterized by insulin resistance, hypertension, hyperlipidemia and an increased risk of cardiovascular disease, Syndrome X is usually associated with obesity (especially abdominal), a high-fat diet and a sedentary lifestyle.10,11,12,13 A result of these factors is high levels of circulating free fatty acids (FFA). In the presence of high FFA concentrations, the body will favor their use as energy, decreasing glucose oxidation, glycogen synthesis, and inhibiting glucose transport.10 The result of this is hyperglycemia. If blood sugar levels are chronically high, insulin will also be elevated, leading to the conversion of the excess blood sugar to other products such as sugar proteins, and fatty acids. These facts alone seem to bolster the idea that carbohydrates lead to health problems. The truth is that a healthy person would need to eat an extremely high percentage of simple carbohydrates (sweets), a high fat diet, be in an energy excess, or overweight to have chronically elevated blood sugar. The average American eats about 34 percent fat and less than 50 percent carbohydrate in their diet. The consumption of mixed meals with these percentages will not allow blood sugar to be chronically high in a healthy exercising individual. There is some evidence that diets high in sucrose or fructose and fat can lead to insulin resistance and obesity in rats. In either case, the solution is a low-fat diet high in complex carbohydrates.14,15 So, how does one become insulin resistant? If one constantly overeats, excess calories are stored as fat. Fat cells then increase in size. The growing fat cell itself becomes insulin resistant and the prevalence of FFA as mentioned earlier will cause the body to favor the use of fat for energy, at the expense of glucose.16 This becomes a viscous cycle that continues to perpetuate itself. The fatness leads to IR. This leads to impaired glucose use. BS levels rise. Insulin levels rise. Cholesterol, TG and blood pressure rise as well. To make matters worse, the impaired ability of glucose to enter muscle cells keeps glycogen stores lower, which can increase appetite, motivating the individual to eat more, increasing fat stores, exacerbating IR, round and round we go.
As numerous studies point out, high-fat diets are strongly associated with obesity, thus insulin resistance and diabetes.16,17,18 Of course eating fat does not make one fat (same with carbohydrate, as explained later) unless consumed in excess of energy requirements. However, it is easier to consume excess energy (hyperphagia) on a high-fat diet due to fat's small volume of food per calorie. Couple the high intake of dietary fat with excess calories and a sedentary lifestyle and it is easy to envision an abundance of free fatty acids floating around in the blood stream. It is much more likely that a high-fat diet leads to the excess consumption of calories, obesity, insulin resistance and eventually NIIDDM than it is that carbohydrates cause insulin resistance and, as a result, obesity. The solution, again, is a diet with the appropriate amount of energy, high in fibrous or starchy carbs, and exercise. In fact, a study of type II diabetics, people with insulin resistance and normal weight people found that three weeks of a highcarbohydrate, low-fat diet and exercise significantly lowered insulin levels.19
