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The two-year study, called DIRECT (Dietary Intervention Randomized Controlled Trial), involved 322 Israeli people who were overweight, or had type 2 diabetes or coronary heart disease. They were asked to follow a low-fat, Mediterranean, or low-carbohydrate diet, and to fill out food frequency questionnaires and give blood samples at several points throughout the study.
At the beginning of the study, blood levels of vitamin D were inversely associated with BMI, meaning the higher the vitamin D levels, the less the person weighed.
Those people who got the most dairy calcium (an average 583 mg per day, the amount in about 2 cups of milk), and those with higher vitamin D levels at six months, lost significantly more weight (about 12 pounds) after two years than people who got less of these nutrients.
The study’s authors commented that while they’re not sure how calcium and vitamin D work to help with weight loss, it’s possible that the effects are due to hormonal influences. Dairy products can inhibit an enzyme that may limit fat cell growth, and they could also increase the amount of fat lost in the stool. Higher vitamin D concentrations might also promote metabolic pathways that favor weight loss or lean body mass.
Since both vitamin D and dairy calcium were associated with weight loss in this study, those who are dairy-sensitive can focus on improving vitamin D status by eating foods rich in D—like egg yolks, fatty fish, and cod liver oil. There are many liquid fish oils on the market cleverly disguised as orange and other-flavored treats. Some cod liver oil supplements contain as much as 400 IU of vitamin D in a single teaspoon. Consult with your healthcare practitioner to decide on the amount of vitamin D that’s right for you, and perhaps get your levels tested if you do not each much dairy or live in a northern latitude that does not get much sun.
(Am J Clin Nutr 2010;doi:10.3945/ajcn.2010.29355)