The concept of the protein shake diet is pretty straightforward. Advertisers claim that by drinking two protein shakes per day over a period of several weeks, you will lose weight and jump-start your metabolism. Replacing meals with shakes may result in a scientific process called thermogenesis. When thermogenesis happens, your body starts burning extra calories.

Protein shakes that are high in fat or protein but low in carbohydrates are supposed to reduce your calorie intake while still making you feel full. Protein shake diets should not exceed one week unless as part of a medically-supervised program.

Any weight loss experienced from a protein shake diet may be temporary and difficult to sustain.

These diets can last anywhere from three days to one full week. Any protein shake diet that lasts longer than that should not involve excessive meal-skipping, which can actually send your body into hibernation mode. This can keep you from healthy weight loss.

The foods that you are restricted from on a protein shake diet might vary according to the specific diet instructions and what’s included in the shake.

During a protein shake diet plan, focus on choosing healthy, fiber-rich foods for the meals you are allowed. High-protein options that will make you feel less hungry and help your digestion work the way it’s supposed to include:

  • whole grains
  • leafy greens
  • bulky vegetables
  • legumes
  • eggs
  • fish

When you’re on a protein shake diet, avoid alcohol, greasy foods, cooking oils, processed grains, artificial sugars, and bleached flour. These foods can “clog up” your system while you’re on a protein shake diet and cancel out the positive effects.

Sample meal plan

Make sure you drink plenty of water while you’re on any protein shake diet. Some protein shake diet programs involve alternating “fat flush” or “cleanse” days with cheat days and shake days. The information here addresses shake days only.

8 a.m.: On protein shake days, a typical meal plan will involve a meal-replacement shake for breakfast. This shake is made of whey protein or a carbohydrate and protein powder mix added to water and ice. Sometimes fat is included in the powder or recommended to be added separately.

10 a.m.: You’re usually permitted a small snack between breakfast and lunch. High-fiber options such as fresh fruit, raw vegetables with hummus, or nuts and seeds are recommended.

12 p.m.: Most shake plans recommend a full, healthy lunch to fill you up and get your energy going. A salad with spinach, avocado, sliced almonds, chickpeas, cranberries, and diced grilled chicken or salmon with balsamic vinaigrette on the side will boost your energy and keep your digestion regular.

3 p.m.: Enjoy another small snack — perhaps a handful of almonds, unsweetened yogurt, or a hard-boiled egg.

6 p.m.: Often, another meal-replacement protein shake is recommended for dinner. Pair it with a low-sugar, high-fiber carbohydrate snack like an apple, some blackberries, or dried, crunchy beans. These options may stave off hunger and help you sleep better. This is because carbohydrates help the body produce serotonin and melatonin, which are important hormones for a restful night’s sleep.

Summary While on a protein shake diet, focus on eating fiber rich foods for the meals and snacks you are allowed. Leafy greens, whole grains, and fish are good options for these meals.

It’s important to choose the shake system that will provide the benefits you’re looking for without too many unpleasant side effects. When you’re on a protein shake diet, you may experience:

  • lightheadedness
  • feelings of dizziness
  • extreme fatigue
  • loose stools
  • constipation
  • stomach cramping
  • irritability
  • headaches

If you take a supplement that’s pure whey protein, you might even develop kidney stones, though this is rare.

Protein shakes contain many different ingredients, and some of them can be artificial preservatives, milk derivatives, or artificial sweeteners. You should be aware of what’s in your protein shakes before starting a diet program.

Vegan protein powders made from pea, hemp, or rice are also options for vegetarians or those who don’t tolerate whey.

Summary Possible side effects of protein diets can include lightheadedness, fatigue, and stomach cramping. Be aware of the ingredients in your protein shake before starting this diet program.

Science offers some evidence supporting protein shake diets via clinical trials. For example, a 2005 study found that high-protein, low-carbohydrate shake mixtures were superior to high-carbohydrate, low-protein shakes. Other research suggests that soy-based formulas may have greater benefits than milk-based ones, though results were not significant.

If you’re a busy person looking to lose weight and you have trouble preparing healthy food or getting to the gym, protein shakes can be an attractive quick fix. However, weight loss from a protein shake diet may not be sustainable. Whether you can keep the weight off depends on your body type, your exercise routine, and your weight loss goals. If you get too hungry and end up eating regular meals in addition to your protein shakes, you can end up gaining weight.

Side effects such as dizziness and increased bowel movements can make your days on protein shakes uncomfortable.

If you replace one or more meals per day with just protein for extended periods, you miss out on valuable nutrients, such as fiber and antioxidants. These are present in whole foods and can prevent nutritional deficiencies and protect your long-term disease risk.

Summary High-protein, low-carb shakes may help you lose weight, but this weight loss may not be sustainable. Healthy food and regular exercise is usually a more sustainable way to lose weight.

Protein shakes may be an effective way to temporarily lose weight for some, but so is a healthy diet and exercise. Any extremely restrictive diet program should only be attempted with the guidance of your physician.

Be careful to read the ingredients on any weight loss supplement before you begin the program, and know your own potential reactions and sensitivities. If you feel extremely dizzy or nauseous, or if your vision gets blurry, stop the program immediately. Drink a quickly digesting carbohydrate-rich beverage, like fruit juice, or eat some fruit, and then call your doctor.