Diet
The main requirement of a dietary approach to weight loss is that total energy intake should be less than energy expenditure.
You should not try heavily restrictive and nutritionally unbalanced diets as they are ineffective in the long term and can be harmful. It is important that you improve your diet even if you do not lose weight, as there are many health benefits from having a nutritionally balanced diet.
A dietitian can suggest changes in your diet, taking into account your food preferences and can make suggestions for your reducing calorie intake. In the longer term, you should move towards eating a balanced diet, consistent with other healthy eating advice. Diets to promote weight loss are generally divided into the four categories below. The effectiveness of each diet in achieving weight loss is also given with trial data below.
This section is aimed at healthcare professionals
1. Low-calorie diets
Low calorie diets usually mean a reduction between 500 and 1000 calories per day, which can result in a 0.5 kilogram weight loss per week. They include the DASH (Dietary Approaches to Stop Hypertension) diet and Weight Watchers among others.
The National Institutes of Health (NIH) reviewed 34 randomised controlled trials to determine the effectiveness of low-calorie diets. The results of their analysis found that these diet lowered total body mass by 8% over 3-12 months.
2. Low-fat calorie diets
Low-fat diets involve the reduction of the percentage of fat in a person's diet. Calorie consumption is often also reduced as a result of reducing a person's fat content. Diets of this type include the National Cholesterol Education Program (NCEP) Step I and II diets.
For example, the Step I diet restricts a person's diet to a total fat of no more than 30% of total calories, saturated fat to no more than 10% of total calories, and cholesterol to less than 300 mg/day. The Step II diet goals were lower for saturated fat (less than 7%) and cholesterol (less than 200 mg/day).
A meta-analysis of 16 trials of 2-12 months duration found that low-fat diets resulted in weight loss of 3.2 kilograms over eating as normal.
3. Low-carbohydrate diets
Low-carbohydrate diets are relatively high in fat and protein. They are very popular in diet and health magazines but are not recommenced by the American Heart Association (AHA) or by the scientific community. Diets of this type include Atkins and Protein Power.
A review of 94 trials found that weight loss was associated with decreased calorie consumption rather than any special properties of reduced carbohydrate consumption. However, no adverse effects from low carbohydrate diets were detected.
A further meta-analysis of 6 randomised controlled trials found no difference between the main diet types (low calorie, low carbohydrate, and low fat), with a 2-4 kilogram weight loss in all studies.
4. Very low calorie diets
Very low calorie diets maintain protein intake while limiting calories from both fat and carbohydrates. They subject the body to starvation and produce average weekly weight loss of 1.5 to 2.5 kilograms. These diets are not recommended for general use as they are associated with adverse side effect such as loss of lean muscle mass, increased risk of gout, and electrolyte imbalances. Very-low-calorie diets (less than 1,000 kcal/day) may be used for a maximum of 12 weeks continuously, or intermittently with a low calorie diet (for example for 2-4 days a week), by people who are obese and have reached a plateau in weight loss.
To prevent complications, a physician must monitor people attempting these diets closely.
