Ever wonder why you don't see those 'drink milk/eat dairy to lose weight' ads anymore?

Yeah, me too. I recently discovered why: it is no longer legal to make this claim. Oh, there are ways around it, sure - now the message is only implied in advertisements, not explicitly stated. In class last week, we examined what used to be the most oft-cited research to support the claim that dairy foods aid weight loss. Let's take a look at:

Zemel MB, Thompson W, Milstead A, Morris K, Campbell, P. Calcium and dairy acceleration of weight and fat loss during energy restriction in obese adults. Obesity Research 2004;12:582-590

This was a randomized, placebo-controlled trial (a very strong study design) that sought to determine the effects of increasing dietary calcium (read: dairy products) during caloric restriction in humans. In other words, does dairy or calcium help weight loss? The trial lasted 24 weeks. The subjects were healthy, obese men and women between the ages of 18 and 60. 34 women and 7 men started the trial (n=41), and 27 women and 5 men actually completed the trial (n=32).

Subjects were randomized into 3 diet groups: high dairy diet (providing 1200-1300mg calcium), calcium-supplemented diet (approx 500mg calcium from food + 800mg from a supplement), and control diet (identical diet to calcium-supplemented diet, except with a placebo supplement). All 3 diets were designed to create a 500kcal/day deficit.

Main outcomes included overall change in body weight, total fat loss (as measured by a DXA scan), fat loss from trunk region (measured by waist circumference and DXA scan). All of this seems well and good. Strong study design, monitoring with reliable tests...the authors even state on p. 584 that "all subjects maintained complete daily diet diaries throughout the study, and compliance was assessed by weekly subject interview, review of the diet diary, and pill counts." Impressive! Too bad they don't report this data. We have no idea what the subjects were actually doing.

Now, for the results: As expected, all subjects lost some weight. For overall body weight (which is the only outcome I will discuss here, for the sake of time and space, and the space-time continuum): the control group lost 6.4 +/- 2.5% of their body weight. The calcium-supplemented group lost 8.6 +/- 1.1%, and the high-dairy group lost 10.9 +/- 1.6% of their body weight. Ok, the high dairy group lost the most weight. Seems like the end of the story, right? I'll get back to that in a minute.

I shouldn't forget to mention some limitations of this study: small sample size (only 32 completers), mostly women, we have no idea exactly what they were consuming during the study because even though it was assessed, those data were not reported.

Now, the lead author of this research wrote a diet book, The Calcium Key, in which he states that study after study has "proven" that low-fat dairy foods work wonders for weight loss, and that you can "increase the amount of weight lost by 70%."

Hmm...

Sure, the control group lost 6.4% of their body weight compared to the 10.9% lost by people on the high-dairy diet. This is an increase of 70%, but what does it actually mean? The control group lost 6.6 kg (14.5 lbs) during the 24 weeks, the calcium-supplemented group lost 8.6kg (18.9 lbs) and the high-dairy group lost approximately 11 kg (24.2 lbs) in 24 weeks. Wow! 1 pound per week!

Remember that all subjects were supposedly eating a diet with a 500kcal/day deficit - this should promote a healthy weight loss of 1 lb per week, no matter how much dairy or calcium one consumes (3500 kcal = 1 lb; 500 kcal x 7 days = 3500 kcal). Perhaps the high-dairy group subjects were simply more compliant with the diet? Again, data not reported, so we don't know.

I hardly think this one study showing us that we can increase weight loss from 2/3 lb per week to a 1 lb per week is grounds for the dairy council plastering posters everywhere (well, they used to be everywhere). Oh, and this research was supported by the National Dairy Council. Not surprising.

What is surprising are the economics and conflicts of interest in this research (i.e. the lead author's employer holds a patent on the claim that dairy consumption improves weight loss!) check out this post from Parke Wilde, who teaches U.S. Food Policy at the Friedman School of Nutrition Science and Policy at Tufts University.