When you're trying to lose weight, it's tempting to want to switch from three solid meals a day to three meal-replacement shakes a day. But while this strategy may trigger a significant amount of weight loss, especially in the beginning, it's difficult to stick to it for the long haul.
The exact amount of weight you can lose depends on different factors, like how much extra weight you're carrying and how committed you are to your goals, but when you only drink three shakes a day, weight loss tends to be only temporary.
The amount of weight you lose when drinking meal-replacement shakes depends on several factors, like your metabolism and what your weight-loss goal is. While weight loss can be significant, especially in the beginning, you're likely to regain the weight with this approach.
What Are Meal Replacement Shakes?
Unlike protein shakes, which get the bulk of their calories from one main source (protein), meal-replacement shakes are designed to take the place of a low-calorie meal. They usually contain a mixture of carbohydrates, protein and fat as well as added vitamins and minerals. They may come in a ready-to-drink liquid or in a powder form that you mix with either water or some kind of low-calorie milk, like almond milk.
One of the biggest benefits of meal-replacement shakes is convenience. They take the guesswork out of figuring out how to design a balanced, low-calorie meal and they're already prepared (or close to being prepared if they come as a powder), so you don't have to spend any time cooking. Other benefits of meal-replacement shakes include:
- Less decision-making
- Less contact with higher-calorie, tempting foods that aren't on your plan
- Pre-determined portion control
- No need to weigh or measure foods
- Easy to transport
- Require little preparation and almost no cleanup
The American Diabetes Association also points out another benefit of meal-replacement shakes that's called sensory-specific satiety. When you eat or drink the same foods (or in this case, meal-replacement shakes) repeatedly, you develop a decreased sense of pleasure to the taste and smell of the food.
When this happens, you start to eat or drink just to satisfy your hunger, instead of looking to excite your taste buds. The theory behind sensory-specific satiety is that when food (or drinks) are monotonous, you're more likely to take in fewer calories.
Weight Loss With Replacement Shakes
The underlying weight-loss principle behind meal-replacement shakes is calorie restriction, although research shows that replacing your meals with nutrient-balanced shakes may have a slight edge over calorie restriction on its own.
According to a report published in Appetite in January 2018, when compared to a regular low-calorie diet, drinking three meal-replacement shakes a day led to greater weight loss (specifically in the form of body fat) and a more significant reduction in food cravings over a period of three weeks.
Another report published in Biotechnology and Genetic Engineering Reviews in August 2013 reviewed studies comparing regular low-calorie diets with meal-replacement diets and found that, when meals were replaced with three shakes a day, weight loss was more significant.
One study showed that, over a period of four months, dieters in the meal-replacement group lost 12.3 percent of their body weight, while dieters in the food group lost around half that, or 6.7 percent.
When dieters who had previously lost 5 percent of their body weight started either a regular low-calorie diet plan or switched to meal-replacement shakes for six months, the regular food group lost an additional 1.3 percent of body weight, while the meal-replacement group lost another 3.2 percent.
Weight Regain With Meal Replacements
While meal-replacement shakes can be a good tool for people who are new to weight loss or who don't have the time to prepare healthy meals on their own, the results are often short-lived.
An August 2013 report in Diabetes Spectrum cautions that, while meal-replacement shakes can help you lose a significant amount of weight, you have to continue drinking them instead of eating meals, to sustain that weight loss for the long term.
The Diabetes Spectrum report also notes that when returning to regular food, many dieters gain the weight back because they haven't effectively learned how to properly control portions. As a result, they tend to underestimate the number of calories they're consuming when they try to build their own meals themselves.
Another reason is that calorie restriction, which is the basis of weight loss on a meal-replacement shake plan, changes your hormones and your metabolism, which makes it difficult to sustain any changes.
When you restrict calories, levels of a hormone called ghrelin go up, while another hormone, called leptin, goes down. This is a problem because ghrelin signals that it's time to eat, while leptin tells you that you're full. If the hormone levels are skewed, you always feel hungry.
Your body also adjusts to calorie restriction by decreasing the number of calories you burn, a process called adaptive thermogenesis. Over time, these factors together become stronger than willpower. That's why many people on a calorie-restricted diet end up gaining the weight back soon after they lose it.
Other Downsides to Shakes
But it's not just weight regain that may make meal replacements an inferior choice to eating whole foods. Suzanne Salamon, MD, a primary care physician specializing in geriatric medicine at the Beth Israel Deaconess Medical Center in Boston, notes that many meal-replacement shakes also contain undesirable ingredients, like sugar, to improve the taste.
Although you may still be able to stay within your calorie recommendations, Dr. Salamon says this is a problem because it can increase the risk for other complications, like diabetes and high blood pressure.
For example, you'll find 19 grams of sugar (in the form of sugar, fructose and high-fructose corn syrup) in the Original Creamy Milk Chocolate meal-replacement shake from SlimFast. The GNC Lean Shake, by comparison, has only 2 grams of sugar, but contains artificial sweeteners (which aren't much better health-wise) in its place.
If you're choosing between commercially prepared shakes, like Slim Fast vs. GNC Lean Shake, you'll have to weigh your options (no pun intended) and determine which type matches up with your own health goals.
In addition to that, meal-replacement shakes are fortified with synthetic vitamins and minerals. In other words, these vitamins and minerals are made in a lab by humans, rather than coming in their natural form in whole foods. Because of this, you may not be able to absorb them as well or as efficiently as you would the vitamins and minerals from fruits and vegetables.
- Appetite: "Effects of 3-Week Total Meal Replacement vs. Typical Food-Based Diet on Human Brain Functional Magnetic Resonance Imaging Food-Cue Reactivity and Functional Connectivity in People With Obesity"
- American Diabetes Association: "Meal Replacement Shakes and Nutrition Bars: Do They Help Individuals With Diabetes Lose Weight?"
- Biotechnology and Genetic Engineering Reviews: "Meal Replacements and Fibre Supplement as a Strategy for Weight Loss. Proprietary PGX® Meal Replacement and PGX® Fibre Supplement in Addition to a Calorie-Restricted Diet to Achieve Weight Loss in a Clinical Setting"
- Harvard Medical School: "Supplemental Nutrition Drinks: Help or Hype?"
- Perspectives on Psychological Science: "Reducing Calorie Intake May Not Help You Lose Body Weight"
- American Psychological Association: "Why Do Dieters Regain Weight?"
- SlimFast: "Original Creamy Milk Chocolate"
- GNC Live Well: "GNC Total Lean® Lean Shake™ 25"