When consumed in moderate quantities, some studies suggest that soy milk can help you lose weight by mimicking hormones in the body that reduce hunger. While any calorie-containing food or beverage can cause weight gain if consumed in excess of caloric needs, high-calorie drinks such as whole cow's milk or liquid nutritional supplements promote more weight gain than soy milk. However, due to soy's hormonal effects, consuming any soy product in large quantities may harm health.
Soy and Weight
A University of Illinois study, presented at the 2007 Experimental Biology meeting in Washington, D.C., found that when lab rats were injected with soy protein, the rats lost weight, despite having unlimited access to food. Researchers theorized that in the mammalian body, soy acts similarly to the metabolic hormone, leptin, which signals to the brain that you're full and should stop eating. Another study, presented at the Annual Meeting of the Society for the Study of Ingestive Behavior in 2010, concluded that soy prevents postmenopausal weight gain in female rats, likely due to its estrogen-like compounds. Lead researcher Michelle Murphy commented that soy may similarly prevent obesity in postmenopausal humans.
Soy Milk Nutrition
Besides potentially promoting weight loss through hormonal mechanisms, soy milk also provides a lot of nutrition for relatively few calories. It is a good source of protein, iron, B-vitamins and heart-healthy unsaturated fats. Soy is an especially effective source of nutrition for vegetarians and vegans -- unlike most plant foods, soy provides all the amino acids needed by the body to make complete proteins. If fortified, soy milk also provides adequate calcium. Furthermore, soy milk is low in saturated fat and cholesterol. According to the USDA National Nutrient Database for Standard Reference, 1 cup of a popular brand of soy milk contains 100 calories, 7 g of protein, 1 g of fiber, 299 mg of calcium, 24 mcg of folate and 119 IU of vitamin D.
Drinks for Weight Gain
Any food or drink containing calories -- including soy milk -- may contribute to weight gain if your total calorie consumption exceeds the amount of calories you burn. However, if you need to put on some healthy weight, you'll see faster results drinking beverages that are rich in both nutrients and calories, such as whole milk or fruit smoothies. You can also add powdered drink mixes that provide extra calories and nutrients to soy milk in order to boost your drink's energy content. Liquid nutritional supplements such as Ensure or Boost may be used to promote weight gain as well. Avoid drinks containing caffeine if you want to gain weight, as these may decrease appetite.
Whether you are looking to gain, lose or maintain weight, do not consume soy milk and other soy products in excess. According to the National Center for Complementary and Alternative Medicine, soy contains compounds similar to estrogen, so there is a chance that soy use could contribute to estrogen-related cancers such as uterine and breast cancer. Further research is necessary to confirm whether long-term use of soy may have negative health consequences, says the NCCAM. While soy milk is likely safe to enjoy in moderation, eating a wide variety of nutritious foods, without placing excessive emphasis on any one food, is the key to good health.