Why do I gain weight when I eat less protein?

Sasson E. Moulavi, MD
General Practice

When you are eating less protein you are eating more fats and sugars. Your body is designed to hunger for energy of about 2500 calories per day. If too few of those calories come from protein you’ll gain weight because you’ll be hungrier eat more and store more fat.

A good example is if you have lots of carbs for breakfast such as pancakes and syrup you’ll be hungrier earlier (and end up eating more at 11 am)  then if you had an egg white omelet. The worse are the pancakes have double the calories then the egg white, that’s why you gain weight.

Some good protein sources are:

  • Egg white
  • Turkey slices
  • Kale, (yes Kale)
  • Smart for life protein bars
  • Kashi cereal
Michaela Ballmann
Nutrition & Dietetics

Protein is a primary factor in satiation and satiety—the feelings of fullness during a meal that cause you to stop eating and in between your meals, respectively.  When you eat less protein than you’re used to (in combination with a low-fiber diet), your body will either want more food at the meal to feel full or you will start feeling hungry again sooner after you eat.  Both of these scenarios with lead you to consume more Calories, which will lead to weight gain.

Daphne Oz
Health Education
Protein forms the building blocks for your body's muscles, and muscles burn fat. Lean muscle burns fat by controlling your basal metabolic rate (BMR), the number of calories you burn when you're doing nothing. Each pound of lean muscle burns 50 calories every day without your having to lift so much as a finger. If you start losing muscle, your basal metabolism will go down and your body will burn fewer calories per day, which could mean weight gain for you.
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The 10-Step Program for Creating a Healthy Lifestyle Plan That Really WorksThe Dorm Room DietRevised and Updated EditionFiguring out how to eat right and stay healthy on your own can be hard! Here is...
Annette Duncan
Nutrition & Dietetics

If you are cutting down on protein you most likely increased carbohydrates or fats in your diet. If it is quick weight gain it could be related to eating a higher carbohydrate diet which would cause you to gain water weight as carbohydrates store water with it when it is stored as glycogen in your body. If you gain the weight, but it takes a week or longer for your weight to increase it could be due to a higher fat intake which has double the calories per gram than protein. 

Alberta Scruggs
Nutrition & Dietetics

Weight gain is something most of us would like to prevent.  To decrease risks of weight gain you should know these basic nutrition facts:

1 gram of Fat = 9 kcalories (Fatty acid is the end product of fat when absorbed by the body.  If not used, it is stored as fat.  This process burns a minimal amount of kcalories.  Remember, fat has double the kcaloreis when compared to carbohydrate or protein).

1 gram of carbohydrate = 4 kcalories (Glucose is the end product of carbohydrate when absorbed by the body.  If not used, it is stored as fat.  Storage of glucose requires water, which weighs a certain amount). 

1 gram of protein = 4 kcalories (Amino acid is the end product of protein when absorbed by the body.  If not used, a small portion can be converted to glucose, then to fat and stored.  This process requires energy or the burning of kcalories.  The remaining portion of the amino acid is changed to ammonia, then to nitrogen, then to urea.  The kidneys remove urea from the body via urination.  This process requires energy or the burning of kcalories.  

So you see, your body uses more energy to use or store the end product of protein;  The body requires water to store glucose in the body, which adds weight;  And, there is minimal energy or kcalories burned to store fat, which has twice as many kcalories. 

Laura Motosko, MSEd, RD
Nutrition & Dietetics
Protein maintains muscle mass which burns calories to prevent weight gain. Protein is one of three macronutrients, the other two being carbohydrate and fat. If you are eating less protein, chances are you may be filling up on carbohydrate which may cause you to retain more water weight, or fat which is more than double the number of calories per gram than protein.
Nadine Pazder
Nutrition & Dietetics
Chances are you end up eating more calories just to feel satisfied. The advantage you get when you include protein in a meal, is that protein digests slowly providing a sense of "satiety" or feeling satisfied. This satiety can help to keep you full between meals and even prevent the need for a snack. When you don't need a snack, it may be easier to keep your calorie intake under control.
Romy Nelson
Nutrition & Dietetics

More lean protein in the diet boosts the metabolism. It has the effect of lowering triglycerides and blood sugar. It also prevents muscle loss when you are eating fewer calories with the intention of losing body fat. Most importantly, it creates a feeling of “fullness” (satiety) so you don’t crave as much sugar. It also helps prevent over-eating calories at night.

Protein builds and maintains muscle mass and is necessary to make hormones, enzymes, and antibodies to protect against disease. It helps maintain fluid and electrolyte balance and can serve as an energy source when carbohydrates and fats are not available.

Anyone can go on a “diet” and lose weight. The problem is that not only does that weight return, but it often comes back accompanied by a few “friends” (i.e. extra pounds).

You can beat the vicious cycle of weight loss and regain in one simple step: consistently add more lean protein to your breakfast, lunch and dinner. Of course, it’s still vital to eat 5-6 small meals a day because frequent, portion controlled eating reduces blood sugar and hunger.

This is not a diet, but a life-long dietary change that is sustainable – which is exactly why it works!



Cassie Vanderwall
Nutrition & Dietetics

Protein is known as the building block of life and is crucial in maintaining healthy muscles, bones, hormones and metabolism. When individuals eat less protein they tend to eat more carbohydrates and fat. A high carbohydrate diet and cause the body to retain water and if the foods are lower in fiber lead to over eating. A higher fat diet is also associated with poor health since it is also lower in fiber, and often higher in artery-clogging fats. It is best to consume all forms of energy in balance to promote a healthy weight. A general recommendation is to make 50% from carbs about 20% from protein and less than 30% from fat.

Brian Tanzer
Nutrition & Dietetics
One possible explanation for this is that protein has a higher thermic effect of food. This means that when you consume protein, the body burns more calories digesting, absorbing and metabolizing protein, than it does with carbohydrates or fat. If you eat adequate protein, and then reduce your protein intake below your required amount, your body will burn fewer calories. If you burn fewer calories, it is possible that you may gain weight.
Jessica Crandall
Nutrition & Dietetics

Lean proteins are a great way to fill up on less calories, which leads to decreased portion sizes and thus weight loss. If you are eating less protein, you tend to eat more carbs. Carbs, especially those that are low in fiber, don't fill you up as much and you tend to want to eat more. Naturally, carbs hold onto some water which might also cause initial weight gain if transitioning from a high protein diet. Speak with your dietitian about appropriate amounts of protein and carbs for you specifically.

Judy Caplan
Nutrition & Dietetics
Because when you eat less protein you are more likely to fill up on carbs. Protein helps keep your blood sugar stable and leads to less sweet cravings. Sweets and other carbs cause more fluctuations in blood sugar and lead to more sweet cravings and often a cycle of over eating and binging.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.