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ABSTRACT
The role of a reduction in dietary fat for weight loss and maintenance should be assessed by evidence based principles giving most weight to randomised clinical trials. Four meta-analyses have examined weight changes on ad libitum fat-reduced diets in intervention trials lasting up to a year, and they all demonstrate a 3-4 kg larger weight loss on the fat-reduced than on the normal-fat diet in normal weight and overweight subjects. The analyses also show a dose-response relationship, i.e. the reduction in percent energy as fat is positively associated with weight loss. Weight loss is also positively related to initial weight - a 10% reduction in dietary fat is predicted to produce a 4-5 kg weight loss in an individual with a BMI of 30 kg/m2. The outcome of the meta-analysis of trials with long-term follow up included only 6 studies, and none of the trials had an active intervention throughout the period. Short-term trials clearly demonstrate that the non-fat diet components are at least as important for body weight regulation as the fat content. Sugar in beverages is less satiating and more obesity-promoting than sugar in solid foods, and replacement of energy from fat by sugar derived from sweetened beverages is not likely to produce weight loss. Protein is more satiating and thermogenic than carbohydrates, and a fatreduced diet with a high protein content (20-25 % of energy) may increase the efficacy of fat-reduced diets markedly. Whereas the glycemic index of the carbohydrate may play a role for cardiovascular risk factors, there is very little evidence to support that low glycemic index foods facilitate weight control. The evidence linking particular fatty acids to body fatness is weak. If anything, monounsaturated fat may be more fattening than polyunsaturated and saturated fats, and no ad libitum dietary intervention study has shown that a normal-fat, high MUFA diet is equivalent or superior to a low-fat diet in the prevention of weight gain and obesity. The current evidence strongly supports a diet with reduced content of fat and sugar-rich beverages, and more carbohydrates rich in fibre and grain (whole grain foods, fruit and vegetables) and protein (lean meat and dairy products) as the best choice for the prevention of weight gain, obesity, type 2 diabetes and cardiovascular disease. The use of a normal-fat, high monounsaturated diet needs more evidence from randomised ad lib dietary intervention trials before it can be recommended to the public.
The role of a reduction in dietary fat for weight loss and maintenance should be assessed by evidence based principles giving most weight to randomised clinical trials. Four meta-analyses have examined weight changes on ad libitum fat-reduced diets in intervention trials lasting up to a year, and they all demonstrate a 3-4 kg larger weight loss on the fat-reduced than on the normal-fat diet in normal weight and overweight subjects. The analyses also show a dose-response relationship, i.e. the reduction in percent energy as fat is positively associated with weight loss. Weight loss is also positively related to initial weight - a 10% reduction in dietary fat is predicted to produce a 4-5 kg weight loss in an individual with a BMI of 30 kg/m2. The outcome of the meta-analysis of trials with long-term follow up included only 6 studies, and none of the trials had an active intervention throughout the period. Short-term trials clearly demonstrate that the non-fat diet components are at least as important for body weight regulation as the fat content. Sugar in beverages is less satiating and more obesity-promoting than sugar in solid foods, and replacement of energy from fat by sugar derived from sweetened beverages is not likely to produce weight loss. Protein is more satiating and thermogenic than carbohydrates, and a fatreduced diet with a high protein content (20-25 % of energy) may increase the efficacy of fat-reduced diets markedly. Whereas the glycemic index of the carbohydrate may play a role for cardiovascular risk factors, there is very little evidence to support that low glycemic index foods facilitate weight control. The evidence linking particular fatty acids to body fatness is weak. If anything, monounsaturated fat may be more fattening than polyunsaturated and saturated fats, and no ad libitum dietary intervention study has shown that a normal-fat, high MUFA diet is equivalent or superior to a low-fat diet in the prevention of weight gain and obesity. The current evidence strongly supports a diet with reduced content of fat and sugar-rich beverages, and more carbohydrates rich in fibre and grain (whole grain foods, fruit and vegetables) and protein (lean meat and dairy products) as the best choice for the prevention of weight gain, obesity, type 2 diabetes and cardiovascular disease. The use of a normal-fat, high monounsaturated diet needs more evidence from randomised ad lib dietary intervention trials before it can be recommended to the public.