Drinking a shake instead of a full meal can provide enough calories and nutrients to work toward gradual weight loss or a healthier diet, but there's no guarantee that it will make a positive difference. Not all meal replacement shakes are nutritionally equal, so it's important to spend some time examining nutrition facts and ingredient labels before you make a choice.
One main health benefits of meal replacement shakes is that they're fortified with a wide variety of vitamins and minerals, so they can successfully stand in for a meal while still meeting your daily requirements. Another advantage is that shakes tend to have fewer calories than full meals, so if your goal is to lose weight, having a shake replace one meal every day can help you reduce your daily calorie count and build up a calorie deficit big enough to produce gradual, consistent weight loss. In a 40-week trial that took place in 2003, Dr. Steven Heymsfield and colleagues found that overweight and obese subjects who used daily meal replacements lost more weight than those who simply followed a low-calorie diet.
There are also some potential risks to using meal replacement shakes. Under USDA rules, shakes are classified as dietary supplements. In an article for the Beth Israel Deaconess Medical Center, Dr. Monica Zangwill points out that supplements are not subject to the same regulations as other foods. Thus, the advertisements and marketing claims they use do not have to be backed up by scientific research, and it can be difficult to get accurate information about them. While some do have genuine nutritional benefits, others contain so much sugar or fat that they are no better than full meals and may even negatively impact your health.
A healthy meal replacement shake needs to keep added sugar and fat to a minimum but contain enough calories to keep you full for several hours. The healthiest shakes will also be high in protein and fiber. A popular meal-replacement shake provides 20 percent of daily fiber and protein requirements with 5 grams and 10 grams, respectively, but it has only 190 calories. A well-known nutritional shake supplies about 250 calories but only 1 gram of fiber and 9 grams of protein; it also packs 18 grams of sugar into each bottle.
Before you use meal replacements shakes as a weight loss strategy or adopt any new diet plan, talk with your physician or a registered dietitian and seek personalized health advice. A smarter, safer way to improve your health in the long term may be to adopt a varied, balanced, low-calorie diet that includes daily servings of lean proteins, fruits, whole grains, low-fat dairy and vegetables. Check the nutrition label for allergens, such as gluten, or milk, if you are lactose intolerant.