Diet Therapy for Weight Loss

Most people who are thinking about losing weight immediately think about going on a diet. It is almost an instinctive response. They may peruse the internet looking for options, much like you are doing now, or they may talk to friends or a doctor about dieting. So firstly, in order to evaluate how effective diets actually are, we need to look at diets and what the scientific community has found in relation to long term diet success.

Popular Diets for Weight Loss

There have been a multitude of well conducted studies carried out to determine the effectiveness of various popular diets on weight loss including diets with calorie restriction, low fat programs with varying combinations of macronutrients, low carb eating plans and the Mediterranean style diet.

Here we will look at just three studies following participants over one to two years, which have been published relatively recently.

Study 1

In 2005 a study was published in JAMA which looked into four popular diet plans for weight loss and cardiac risk factor reduction¹.

In a single-centre randomized trial a total of 160 participants were randomly assigned to either Atkins (carbohydrate restriction, n=40 people), Zone (macronutrient balance, n=40), Weight Watchers (calorie restriction, n=40), or Ornish (fat restriction, n=40) diet groups. After 2 months of maximum effort, participants selected their own levels of dietary adherence.

After correcting for participants who discontinued the study, the average weight loss at 1 year was:

2.1 kg for Atkins (21 [53%] of 40 participants completed),
3.2 kg for Zone (26 [65%] of 40 completed),
3.0 kg for Weight Watchers (26 [65%] of 40 completed) and
3.3 kg for Ornish (20 [50%] of 40 completed).

Greater effects were observed in study completers, but there was significant deviations from the average losses in all diets.

Study 2

A 2008 study compared the effectiveness of weight-loss diets over a 2-year trial period². They randomly assigned 322 moderately obese subjects (average age, 52 years; average body-mass index, 31; male 86%, female 14%) to one of three diets:

low-fat, restricted-calorie;
Mediterranean, restricted-calorie; or
low-carbohydrate, non–restricted-calorie.

The average weight losses at two years, corrected for the drop-outs were:

2.9 kg for the low-fat group,
4.4 kg for the Mediterranean-diet group, and
4.7 kg for the low-carbohydrate group

Among the 272 participants who actually completed the study, the average weight losses were:

3.3 kg,
4.6 kg, and
5.5 kg, respectively for each diet.

Study 3

The most recent study appearing in The New England Journal of Medicine in 2009 seemingly finished the controversy about the differences in levels of success between fashionable dieting programs³.

This study followed 811 overweight participants who were arbitrarily divided into four groups allotted to pursue a reduced calorie diet. Each of the four diet plans cut down around 750 calories from the participants normal diet. The targeted percentages of energy gained from carbs, protein and fats in the four diets were:

weight loss groups

The diets were designed to allow the investigators to compare average protein versus high protein, low fat versus high fat and the comparison of highest and lowest carb content. Every subject was offered individual and group counselling instructions for the two years of the study.

This is what they discovered:

• 645 participants (80%), completed the two year trial, with a mean weight loss of 4Kg.
• After 6 months, participants allotted to each diet had lost an average of 6 kg, which constituted 7% of their initial weight.
• After 12 months, all groups, on average, slowly regained body weight.
• After the two years was complete, each group had lost – and regained – approximately the same amount of weight, regardless of the group.
• In those assigned to a diet with 20% fat and those assigned to a diet with 40% fat the mean weight loss was the same (3.3 kg for both groups).
• At the end of the two years, weight loss remained similar in those who were assigned to a low protein diet (15%) vs those assigned to a high protein diet (25%) (3.0 and 3.6 kg, respectively).
• After two years, those assigned to a diet with 65% carbohydrates and those allotted to a diet with 35% carbohydrates had losses of 2.9 and 3.4 kg, respectively.

Between 6 months and 2 years into the trial, people found sticking to their diet difficult and some of the participants reverted partly to their old eating habits despite the extensive counselling available. Satiety, hunger, satisfaction with the diet, and attendance at group sessions were similar for all diets.

This was a large, well conducted trial carried out for an extended period of time, giving confidence that these results are significant.

Bottom Line

Although we have only reviewed three studies, these three studies do indicate strong and consistent evidence that over an extended period of time, people initially lose weight and then begin a slow weight regaining process, to leave only modest overall weight losses after one to two years.

These studies were all carried out within a clinical environment, which results, typically, in more success that people achieve out in the real world.

Clearly, more is needed than dietary therapy for successful, sustainable weight loss. Lets look at Diet and Exercise to Lose Weight, to see if the medical world has had more success with this approach.

Sources:

(1) Dansinger ML, Gleason JA, Griffith JL, et al. Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction: a randomized trial. JAMA. Jan 5 2005;293(1):43-53. PMID: 15632335. Full text.

(2) Shai I, Schwarzfuchs D, Henkin Y, et al. Weight Loss with a Low-Carbohydrate, Mediterranean, or Low-Fat Diet. N Engl J Med. 2008 Jul 17;359(3):229-41. PMID: 18635428. Full text.

(3) Sacks FM, Bray GA, Carey VJ, et al. Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates. N Engl J Med. 2009 Feb 26;360(9):859-73. PMID: 19246357. Full text.