Types Of Diets: Which Diet Really Works? Low-Fat And Low-Carb Diets

Weight loss and dieting is a big business these days. Good books on dieting are making millions of dollars in sales, and weight loss coaching is rapidly developing as a profitable business. Many advertised approaches to the weight loss, however, have not been subject to scientific scrutiny. In fact, 75% of popular diets are not scientifically tested. This article outlines some established scientific facts about two mainstream approaches to weight loss based on restricting the intake of fats and carbohydrates.

Low-Fat Diets

The World Health Organization Study Group currently recommends that 15% of the daily calorie intake be derived from fat. Therefore, in practical terms, a low-fat diet would be one diet in which ≤15% of daily calories are derived from fat, preferably with an intake of similar amounts of saturated, monounsaturated  and polyunsaturated fatty acids.

The reported increase in the consumption of fats across the world has been positively associated with a number of undesirable events, such as increased incidence of cardiovascular disorders, increased incidence of certain cancers and an overall rise in mortality resulting from cardiovascular complications.

Low-Fat Diets Substantially Reduce Cholesterol Levels

Conversely, interventional studies conducted with the aim of identifying the outcomes of reducing fat consumption (e.g.: the Heidelberg Trial, the Lifestyle Heart Trial, the Pritikin Longevity program) have produced impressive data. For instance, subjects participating in the Heidelberg Trial, after 6 years had their LDL cholesterol (so-called “bad” cholesterol) levels reduced by 6% in the intervention group and elevated by 1% in the control group. HDL cholesterol (“good” cholesterol) levels were elevated by 14% in the intervention group and 12% in the control group.

As for the specific effects on body weight, data appear promising as well. The Women’s Health Trial reported reductions in dietary fat intake from 37% to 22% of energy, a change resulting in a 3-kg weight loss over a 2-year period. Researchers reported that intensive instruction to maintain a low-fat diet resulted in reduction of fat intake from 39% to 22% of calories and was accompanied by a 3.2-kg weight loss in 6 months, although this was reduced to 1.9 kg at the end of 2 years study period (the control group lost 0.1 kg after 2 years). However, long-term data suggesting very low fat diets alone will sustain long-term weight loss is lacking.

Low-Fat Diets: Some Potential Risk Factors

So while the results of these studies appear impressive, many questions remain about long-term efficacy and safety. One of the concerns with adopting a low-fat diet is the potential risk for nutrient deficiency. It is important to note that the nutrient adequacy of very low fat diets is highly dependent on individual food choices. Very low fat diets can include nutrient-dense foods such as fruits, vegetables, and whole grains, or more the modern fat-free and low-fat alternatives to traditionally high-fat foods, such as snacks and desserts, which are not so nutrient-dense.

Recommending a lower limit to the fat intake is controversial because of the difficulty in balancing the efficacy of a very low fat diet in decreasing plasma cholesterol levels against the risks of nutrient inadequacy or other adverse effects. Certain populations, such as growing children, pregnant women, lactating women, and the elderly, have special needs for essential fatty acids and caloric density and, as such, should not abide by these diets.

Very-low-fat diets have a very high carbohydrate and fiber content. The American Heart Association cautions against the use of such diets because their high carbohydrate content can increase triglyceride levels. Additionally, the diets can contain over twice (40–70 g/d) the recommended amount of fibers. High fiber intakes can decrease the absorption of zinc, calcium and iron. Complaints of abdominal fullness have also been reported.

See Also: Top 10 Foods To Shift Belly Fat

Not All Fats Are The Same

Moreover, many lines of evidence indicate that the type of fat is very important to long-term health. For instance, replacing saturated and trans with natural vegetable oils can greatly reduce the risk of heart disease and diabetes. In the Nurses’ Health Study II it was seen that women who consume high amounts of red meat and high-fat dairy foods during their early adult years are at increased risk of developing breast cancer. Making good dietary choices does really matter, but it might be the type of fat, not the amount, that is most important. 

Low-Carbohydrate Diets

The term “low-carbohydrate diet” is loosely applied to both the diets that significantly restrict carbohydrates to less than 20% of caloric intake and to the diets that merely limit the carbohydrate intake to less than the recommended amounts (typically less than 45% of caloric intake).

Although it is difficult to estimate the number of individuals following a low-carbohydrate regimen (carbohydrates between <10% to 30% of daily energy intake), the popularity and number of low-carbohydrate diets reflect a high level of interest. Certain dietary plans such as the Atkins diet minimize total carbohydrate consumption without fat and energy restriction while many reduce carbohydrate intake and alter macronutrient composition (i.e. Sugar Busters and Zone diets). Other regimens like the South Beach diet combine various strategies across different phases to modulate carbohydrate consumption. The long-standing rationale underlying carbohydrate restriction is that reduced carbohydrate intake and the resulting ketosis (i.e. obtainment of energy from adipose tissue) will decrease basal insulin levels thereby promoting lipolysis and reducing lipogenesis, eventually leading to the fat loss.

Multiple Benefits Of Low-Carb Diets Are Well Documented

Weight loss while following a low-carbohydrate diet is thought to result from a combination of factors: the satiating effect of protein, increased energy expenditure, appetite suppression from ketosis, increased bound-water loss and food choice restriction. A growing body of evidence indicates that low-carbohydrate diets might be more effective for short-term weight loss than low-fat diets, while longer-term studies show that differences between the two regimes dissipate after 1 year.

The particular characteristics of a low-carbohydrate diet are associated with both favorable and unfavorable effects on the body that go beyond possible weight loss.  The most dramatic and consistent lipid response to a low-carb diet is a moderate to large decrease in fasting triglyceride levels and postprandial triglyceride responses to a fat-rich meal. For example, the researchers who conducted the clinical trial reported that triglyceride levels had decreased by 28.1% in a population following a low-carbohydrate diet.

Moreover, in this clinical trial the treatment with this type of diet was associated with an improvement in insulin sensitivity, in the sense that progressively less insulin was secreted to maintain the same blood glucose concentrations.

Long-Term risks Of Low-Carb Diets

Nevertheless, these results should not be interpreted as precluding the possibility of harm from low-carbohydrate diets through changes of serum lipid profile. In one study, increases in low-density lipoprotein cholesterol levels of more than 10% were seen in 30% of subjects in the low-carbohydrate diet group and only 16% in the low-calorie diet group, and 2 participants in the low-carb diet group were withdrawn from the trial because of important adverse effects on blood lipid levels. Furthermore, people on low-carb diets consume a large amount of saturated fats, representing 17% of total energy intake, which is almost double the current recommendation of health organizations. Saturated fats are associated with increased levels of LDL cholesterol, a well-known risk factor for coronary artery disease. Although the beneficial effects of low-carbohydrate diets on serum lipid levels may offset the negative effect of increased levels of saturated fat in the short term, the impact of the diet on low-density lipoprotein cholesterol levels over the long term (2–5 years) must be evaluated.

Finally, two other studies produced evidences that low-carb diets are typically nutritionally poor, with low amounts of vitamins A, B6 and E and of folate, calcium, magnesium, iron, potassium and dietary fiber. This is because, overall, low-carbohydrate diets are usually low in fruits and vegetables, dairy products and whole grains. These dietary patterns, if maintained over long periods of time, increase the risk of a variety of chronic diseases, including hypertension and cancer. High-protein diets affect renal function and can place greater demands on the kidney and liver for metabolizing and excreting excess urea and ammonia. They may be a health hazard for patients with renal or liver impaired functions in general, particularly patients who are also diabetic.

See Also: The facts about Atkins Diet: Pros and Cons

Eventually, the success in losing weight depends on the adherence to the proper eating plan. Long-term sustainable weight loss, however, is hardly ever achieved without serious lifestyle modifications. Sedentary lifestyle is one of the major reasons people become fat, and dieting alone is unlikely to be successful without incorporating physical activities in everyday life. This is something to keep in mind regardless of what type of diet you chose.