Fats, Proteins or Carbohydrates – What’s the best combination for a weight-loss diet?

When choosing a diet to lose weight it seems that rather than eating a balanced healthy diet people choose to follow the latest celebrity endorsed diet programs with low scientific rationale but high novelty factor and media hype. These diets often emphasize eating high levels of protein, fat or carbohydrates.

There are scientific trials that have shown low carb-high protein diets provides more weight loss than high carb-low fat diets, but equally there are a number of studies that don’t show that effect. One study has shown that a low fat diet is better than a moderate fat diet, whilst others have shown that a moderate fat, Mediterranean style diet is superior to a low fat diet.

Whatever the diet, there is short term research out there to both support and disprove it. Now research published in the New England Journal of Medicine has examined the advantages of high fat, protein or carbohydrate diets over 2 years. Unlike other diet studies this one had a large number of participants (811), involved a high number of men (40%), and had good adherence to the diet by the participants (80% completed the 2 years study compared to normal diet studies where 40% drop out).

The participants were aged 30-70 years old with a BMI of 25-40. They were randomly assigned to one of four diets, with the percentage of energy from each food source being:

• Diet 1: 20% Fat; 15% Protein; 65% Carbohydrate
• Diet 2: 20% Fat; 25% Protein; 55% Carbohydrate
• Diet 3: 40% Fat; 15% Protein; 45% Carbohydrate
• Diet 4: 40% Fat; 25% Protein; 35% Carbohydrate

Each person was given a diet with a deficit of 750 calories a day as calculated from their resting energy expenditure and activity levels. Also 90 minutes of moderate exercise a week was prescribed.

Other goals of the diets were they should have

• 8% or less saturated fat,
• at least 20% fibre,
• 150mg or less of cholesterol per 1000kcal,
• carbohydrate foods with low glycemic index.

Typically weight loss is greatest 6-12months after starting a diet followed by a subsequent steady regain of weight. In this study at 6 months participants in each diet had lost an average of 6kg (7% body weight). The participants in each diet reported a reduction in calories of around 400kcal, although a mean weight loss of 6.5kg at 6 months corresponds to a reduced daily intake of approx 225kcal.

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