The Connection between Calcium and Weight Loss
There is an article in Psychology Today describing a study where overweight people were put on a calorie restricted diet and randomized to three groups: low calcium supplements (pills), high calcium supplements, and dairy supplements at a level of calcium equal to the high calcium supplement group.
On a calorie restricted diet, the low calcium group lost 6.4% of their body weight. The high calcium group lost 7.7%. But, surprisingly, the dairy group lost 10.9%, and specifically in their abdomen.
Savvy readers might suspect that since all groups ate the same number of calories, maybe the dairy group ate dairy at the expense of something "worse" that the other groups may have eaten. This certainly is possible, but it would not explain why the fat loss was targeted in the abdomen, and not all over the body.
However, before going to buy a cow, there are a few things to keep in mind:
First, the effect is (so far) specific to yogurt, and maybe milk. Cheese is excluded.
Second, the effect is most pronounced - or only seen - in people who are overweight and beginning a diet with a calorie restriction. Merely adding yogurt to your current diet will not be enough.
Third, these effects are only seen in those who have low calcium diets. This appears to be very important, as overweight people already on high calcium diets don't lose weight faster with dairy. Therefore, adding yogurt even without calorie restriction may help you lose weight if you are low on calcium.
The connection between calcium and weight is that low calcium causes the body to release a hormone, calcitriol, which is the active form of Vitamin D. The article explains that calcitriol stimulates fat synthesis and prevents fat breakdown, so logically reducing calcitriol would have the opposite effect. While this is good in theory, it's not so simple, and the effect is massively outweighed by anything else that would affect fat synthesis.
The body doesn't absorb calcium very well. It should be taken with food, and anything more than the standard 500mg per dose is probably wasted. In this context, eating dairy makes sense, especially if you need calcium supplementation.
Finally, a large epidemiological study found no effect on weight of eating more dairy over 12 years. However, this study used both overweight and normal weight men.
Linking it back to depression, SSRIs may possibly have a long term effect of bone loss in the hip, especially at the greater trochanter of the femur, in older women. The effect seems lessened with tricyclic antidepressants and SSRIs. Why this would happen is not clear, but it's yet another reason to increase your calcium intake.