n4 nutrition

It's not what you eat. It's how much

Diets, General Nutrition, Weight - Body Shape and Composition, Healthy Eating, Eye Health
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This is the finding from the latest research on the effect of four weight loss diets which differ in fat, protein and carbohydrate composition.

The study, published in the highly respected American Journal of Clinical Nutrition last month, examined changes in body composition of 811 men and women who ate 1 of 4 different diets over a two year period. Participants were between 30 and 70 years of age and had a body mass index (BMI) between 25 and 40. A BMI above 25 is deemed as overweight and a BMI over 30 is termed obese.

The diets tested in this study included:

1.     a low fat (20% of energy), average protein (15% of energy) diet

2.     a low fat (20%), high protein diet (25%)

3.     a high fat (40%), average protein diet (15%)

4.     a high fat (40%), high protein diet (25%)

Each diet had varied levels of carbohydrate (35% to 65% of energy) and was restricted in energy. Subjects were measured for changes in total body fat, abdominal fat, hepatic (liver) fat and lean body mass (muscle).

The study was a randomized control trial (RCT), the gold standard for scientific research, and thus of high quality. An RCT means people have been randomly assigned to a group. Chance alone determines which treatment group a person is allocated to which eliminates selection bias and other confounding factors. In other words, all other possible explanations for the research outcome, apart from the effect of the treatment being studied, have been removed. RCTs therefore provide the most reliable evidence of cause and effect.

The study found that the reduction in total energy intake was the most important determinant of fat loss - it did not matter which diet group a person had been assigned to. This is consistent with findings from previous research of a similar nature. There was also no benefit to be found from eating a high protein diet over an average protein diet on lean body mass preservation. Finally, there appeared to be no effect from the fat content of the diet on total body fat loss. This research is also believed to be the first evidence that the macronutrient profile of the diet does not have an effect on changes to hepatic fat during weight loss.

This RCT provides further evidence that the loss of body fat including abdominal and hepatic fat are dependent on energy or kilojoule (kJ) intake. It appears that the macronutrient composition of the diet does not play a significant role in body composition changes in individuals who are overweight or obese.

What does this mean?

Weight loss is simply about eating less energy than is expended. We just need to watch our overall energy intake to make sure it does not exceed our needs. This doesn’t mean weight loss is easy but we don’t need to spend lots of money on fad diets, special foods and diet books to do it. As Louise Foxcroft writes in her new book about the history of dieting, “The diet industry is all about exploitation and profit”. It’s far better to manage weight loss by committing to a healthy lifestyle which focuses on a balanced diet of healthy foods and physical activity most days of the week. A nutritionist or dietitian can provide help and support with initial weight loss and to sustain the benefits long term.

AuthorEmily Greenfield

Further reading:

Effects of 4 weight-loss diets differing in fat, protein, and carbohydrate on fat mass, lean mass, visceral adipose tissue, and hepatic fat: results from the POUNDS LOST trial: 

It's not what you eat. It's how much