A study published in the American Journal of Clinical Nutrition found that people who drank a cup and a half of MILK a day lost nearly twice as much weight as those who consumed just a half a cup. How come? The milk drinkers had higher levels of vitamin D, which is associated with weight loss. Any nutritional deficiency slows your metabolism, causing you to hold onto weight. And since nearly half of Americans lack adequate D, dairy products can counter the effect.