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Healthy Weight: What Randomized Control Trials Show

The majority of these studies demonstrated either an augmentation of body weight loss or fat loss with caloric restriction or a prevention of weight gain.^1-17 Three of the aforementioned studies found no association,^7,10,13 but the findings from these three studies may be due to the threshold effect.

The strongest evidence to date of a link between weight and calcium and/or milk product consumption originates from the landmark Women’s Health Initiative (WHI) Study, published in 2007.¹³ This was a randomized, double-blind, placebo-controlled trial of 36,282 postmenopausal women followed for three to seven years. The objective of this study was to test the hypothesis that calcium and vitamin D are associated with less weight gain in postmenopausal women. This study demonstrated that calcium and vitamin D helped prevent or limit weight gain, primarily in women with baseline calcium intakes below the recommended intake of 1,200 mg per day.¹³

• 36,282 postmenopausal women (50 to 79 years, mean body mass index = 29) were randomized to receive either 1,000 mg of elemental calcium (in the form of calcium carbonate) plus 400 IU of cholecalciferol (vitamin D) or a placebo;
• At baseline, only 39.6% of the women met the current recommended intake of 1,200 mg calcium/day from diet and supplements combined;
• After 3 years, women taking calcium plus vitamin D had a lower risk of gaining weight in both small amounts (1 to 3 kg) and moderate amounts (> 3 kg) and were more likely to remain stable (± 1 kg) or lose weight (> 1 kg);
• Those who received supplements and whose baseline calcium intake was < 1,200 mg/day had an 11% lower risk of gaining both 1 to 3 kg and > 3 kg compared to those whose baseline calcium intake was ≥ 1,200 mg/day;
• Women who had baseline calcium intakes of ≥ 1,200 mg/day saw no significant benefit with calcium and vitamin D supplements.

In another randomized controlled trial of 45 obese individuals over 17 years, 3 very low calorie diets were compared for 16 weeks.¹

• A control diet consisting of 812 kcal with a variety of conventional foods;
• A milk-only diet that consisted of 812 kcal and a combination of full-fat cream or semi-skimmed milk and unsweetened yogurt;
• A milk-plus diet of 1,338 kcal that was similar to the milk-only diet but allowed for 7 extra foods that were self-selected;
• The milk-only and milk-plus diets were significantly associated with greater weight loss and compliance with the diet.

The results from this study are as follows:

• The mean weight loss in the milk-only diet was 11.2 kg in 16 weeks compared to 2.6 kg for the conventional diet;
• Those on the milk-plus diet lost 8.2 kg over 16 weeks, even though their energy intake was nearly 40% higher than the conventional or milk-only diets.

Similarly, in another study, 34 mostly female obese adults were randomized over 12 weeks to:⁸

• A control diet consisting of 0 to 1 servings of milk products/day (providing 400 to 500 mg calcium);
• A yogurt-supplemented diet with three 6 oz./day servings of fat-free yogurt (providing 1,100 mg calcium).

Both diets were reduced in calories by 500 kcal to encourage weight loss of 1 pound per week. Calcium in both diets was derived from food sources (mainly milk products).

The results of this study indicated that:

• Participants on the yogurt-supplemented diet lost significantly more body weight (22% more) and fat mass (61% more), particularly central fat, than those on the control diet;
• Participants on the yogurt-supplemented diet also lost significantly more trunk fat and less lean body mass and had a lower body mass index than those in the control group.

Other studies by Zemel and colleagues also demonstrated that higher milk product intakes accelerate weight and fat loss during energy restriction in obese adults.^2,9

In a randomized controlled trial of 259 overweight adults (mean age 55 years) with type 2 diabetes, a higher consumption of milk-derived calcium was associated with significantly greater weight loss despite higher energy intake. A higher consumption of milk calcium was also significantly associated with a lower body mass index and lower triglyceride levels.¹⁴

Conversely, other studies did not find a significant difference with higher versus lower intakes of calcium and/or milk products and weight loss^3,7,10 or prevention of weight gain in at-risk groups, such as growing children and/or adolescents^18-20 or postmenopausal women.¹² However, it is important to note that there are several limitations that have been reported in these studies, some by the authors themselves. For example, Harvey-Berino¹⁰ and colleagues, who found no significant differences between the high milk product group and the control group, point out in their often-cited study that a sample size of308 individuals was needed to detect the 1.2-kg difference they found, as shown by post-hoc power calculations.¹⁰ In other words, with only 44 individuals, this study clearly lacked the power to detect an otherwise clinically meaningful difference.

The majority of randomized controlled trials, including a landmark study, demonstrate that milk products or components, such as calcium, have a beneficial impact on body weight regulation.

Keywords: healthy weight, health studies

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