Many different types of diets have all promised permanent weight loss.
Credit: Flickr/William Hartz

Many different types of diets have all promised permanent weight loss.

There are as many diets geared toward weight loss as there are choices at a buffet

Every diet, whether it's high carb, low carb or in between, promises permanent weight loss

But the question is, do any of them really work in the long term?

A quality study published in 2009 looked at four different diets over a two-year period and compared the results.

The study randomly assigned 811 overweight adults to one of four diets consisting of these macronutrient ratios:

  1. A high carb, moderate fat, low protein diet of 20% fat, 15% protein and 65% carbohydrates
  2. A high carb, moderate fat, moderate protein diet of 20% fat, 25% protein and 55% carbohydrates
  3. A high fat, moderate carb, low protein diet of 40% fat, 15% protein and 45% carbohydrates
  4. A high fat, moderate protein, low carb diet of 40% fat, 25% protein and 35% carbohydrates

Each of the diets was made up of similar foods and all met the guidelines for cardiovascular health. They all included eight percent or less of saturated fat, 20 grams or more of fibre, a maximum of 150 mg of cholesterol per 1,000 calories, emphasized low glycemic carbohydrate foods and represented a 750-calorie reduction in each individual's total daily intake.

So the main difference between the diets was simply the ratio of macronutrients (fats, carbs and protein).

Participants received group and individual instructional sessions over a two-year period to teach them about the diet and help them stick to it.

Weight Loss Results

All of the diets showed weight loss with most of that weight loss occurring in the first six months. After 12 months all of the groups had begun to put weight back on. But 23% of the participants, regardless of which group they were in, still continued to lose weight from six months to two years.

The average weight loss was between three to four kilograms over two years, and each diet was successful in achieving this outcome. Some other interesting results after two years:

  • 31% to 37% of the participants had lost at least five percent of their initial body weight
  • 14% to 15% of the participants in each diet group had lost at least 10% of their initial weight
  • 2% to 4% had lost 20 kg or more

Take Home Advice

If losing weight is one of your goals, here's what you can take away from the results of this research:

  • Cutting back on your calories is more important than the particular composition of fats, protein and carbs of any diet.
  • Having some support or direction can help you stick to a diet, so working with a professional such as a nutritionist or trainer can make a difference.
  • Choosing a diet that suits your individual tastes and lifestyle is important, so you need to be able to individualize the diet.
  • Keeping track of your eating can help.
  • Changing your behaviour is probably more important than the specific type of diet you follow.
  • You'll probably lose most of your weight within the first six months of a diet and you can expect to gain some of that weight back in the long term. But don't get discouraged by this. Overall, you can still expect to weigh less in the long run if you continue to eat fewer calories than you're burning through daily living and exercise.