Why does a high-fat diet cause more weight gain than a high-protein diet?

Heather Rudalavage
Nutrition & Dietetics

High fat foods tend to be "calorically dense" foods. That means you get a lot of calories in a smaller amount of food. It's easy to over eat when you are eating a lot of food that has a high fat content. Foods that are high in lean protein (high protein, low fat) are less calorically dense and also tend to be low in carbohydrates. Most Americans get enough protein in their diet, so protein supplements are usually a waste of money but also contain unnecessary calories. Eating a balanced diet with lots of whole grains, fruits, vegetables and lean meats is a good way to stay healthy.

Linda Kaminski
Nutrition & Dietetics

Ultimately, it depends on your total daily calorie intake. Gram for gram, fat has over twice as many calories as protein (9 calories for fat vs. 4 calories for protein). The more calories you take in, the greater your risk of weight gain. Therefore, if you consume a high fat diet, you are likely consuming a higher calorie diet as well. High protein diets are known to suppress appetite, which will likely allow you to consume less calories overall, thereby increasing your chances of losing or maintaining your current weight. However, high protein diets can be stressful on the body and hard to maintain long term, making it more likely to gain weight back once normal eating habits are resumed. A balanced, calorie controlled diet is best and easiest to maintain long term, containing moderate amounts of all major nutrients, including carbohydrates, fats, and protein.

Janis Jibrin, MS, RD
Nutrition & Dietetics
The main reason a high protein diet helps people lose weight is because people wind up eating fewer calories than they did before they started the diet.  Most high protein diets require that you drastically limit carbohydrates, and if you eliminate bread, pasta, cookies, cake and the like, it's no surprise that you'll lower calorie levels and lose weight.  Protein is also satiating, meaning it helps you feel full and quells appetite, always a plus for weight loss.
On the other hand, you're not cutting out any food groups on a high fat diet, so you don't get the automatiic calorie drop.  And because fat has more than double the calories per gram as protein (or carbohydrates) it's easy to rack up calories on a high fat diet.
That said, I don't recommend either type of diet.  My gripe against high protein diets (like Atkins) is that you not only restrict unhealthy carbs like cookies, but you cut out whole grains, certain fruit and other healthy carbs.  Instead, I recommend that you limit these foods, but not cut them out.  If you're trying to lose weight, have about 5 servings of whole grains or starchy vegetables, like potatoes.  A serving is 80 calories, and is about a half cup of cooked pasta, sweet potatoes, or 1/3 cup rice or legumes.  As for cereal, check labels to see the cup measure of 80 calories.
As for the amount of fat in your diet, 30 to 35 percent works well for most people--that's moderate, not high.  Most of your fats should be "good" fats--rich in mono- and poly-unsaturated oils, foods like olive oil, canola oil, flaxseeds and other seeds, nuts and avocados.  Also make sure to eat fatty fish like salmon and sardines 3 times a week for omega-3s (a type of poly).  If you're trying to lose weight, aim for about 5 to 6 fat servings daily; a serving is 45 calories, such a teaspoon of oil or a tablespoon of nuts.
Meanwhile, have about 6 to 8 protein servings daily--a serving is about 50 to 65 calories such as an ounce of seafood, poultry or meat (limit red meat to no more than once weekly); one egg; 2 - 4 ounces tofu. 
Round out your diet with 2 servings (90 - 100 calories) of nonfat milk or calcium-fortified soymilk, nonfat or lowfat yogurt, and have plenty of vegetables and at least 2 fruits daily.
Brian Tanzer
Nutrition & Dietetics

The two main reasons for this is fat contains 9 calories per gram and protein 4 calories per gram. The second reason is protein has a higher thermic effect of food (TEF). TEF is the amount of calories the body uses to digest, absorb, and metabolize food. The combination of a higher calorie content and lower TEF helps explain why a high-fat diet typically causes more weight gain than a high-protein diet.                       

Julieanna Hever, RD
Nutrition & Dietetics
Fat has more than twice the amount of calories per gram as does protein. Additionally, foods that are high in fat usually (but not always) tend to come loaded with sugars and other processed foods that contribute to weight gain. However, a high-protein diet is not ideal for weight loss either because it is harmful to your health in the long run. We only require about 10% of our calories to come from protein. Any more-especially from animal sources-increases your risks of excess weight, obesity, and most chronic diseases. Ideally for weight management and optimal health, consume the majority of your calories from whole plant sources of carbohydrates in conjunction with a small amount of protein and fat. Eating a whole food, plant-based diet makes it easy because you don't ever need to calculate or quantify any numbers. Just eat whole plant foods when you are hungry, stop before you are full, and you will effortlessly maintain your ideal body weight.
Jessica Corwin
Nutrition & Dietetics

Fat grams provide us with 9 calories per gram, an amount more than double that found in carbohydrates and protein at 4 calories per gram. Therefore we are able to consume far more calories in a bowl of high fat food than if it were a bowl filled with lean proteins or whole grains. 

Research published in the Journal of Obesity found evidence that a diet rich in lean protein is better at promoting satiety than a diet high in fat. This means that the protein helps us to recognize that we are full more quickly; therefore we have to eat less.

The other big factor to consider is that high fat foods do not contain fiber, a food component that helps us feel full. Fiber is found in whole grains, fruits, vegetables, and protein rich nuts, seeds, and beans (not in animal products). Further studies have found that fiber will not only help to maintain our weight but it may reduce our risk of metabolic syndrome, heart disease, and certain cancers. 

With this type of evidence, I would be quick to ditch the fried foods and sweet treats and seek out more beans, nuts, and seeds for a true boost in health. Blackbean quesadilla, anyone? ;)


Higher Protein Intake Preserves Lean Mass and Satiety with Weight Loss in Pre-obese and Obese Women. Obesity (2007) 15, 421–429; doi:10.1038/oby.2007.531


Judy Caplan
Nutrition & Dietetics

A high fat diet can be misleading. Some high fat diets which contain healthy fats, plus lean protein, fruits, veggies, and whole grains, can actually allow you to lose weight. It depends on the kind of fat and total calories.





Sheri L. Emma, MD

There are three main food categories:  fat, protein, and carbohydrates. Fat contains 9 calories per gram, whereas protein and carbohydrates generally contain about 4 calories per gram. Therefore, fat has almost double the calories per unit. 

It seems then that avoiding fat would be all that is required to lose weight. However, there is a reason why the "fat-free" diet fad of the 90's was not very successful. The concept seems easy, that if you don't eat fat you won't get fat. The reason it's not that simple is: it isn't fat alone that causes fat; it's carbohydrates in excess as well. Carbohydrates are the most efficient source of energy for the human body. It's meant to be used for energy as much as possible at the time of consumption, and any excess carbohydrates consumed are then stored for later. How are they stored?  They are largely stored as fat.

So let's turn to protein. The first purpose of protein is for the amino acid building blocks of the protein. Our bodies need protein every day for growth and repair. The second purpose of consumed protein is to provide fuel, or energy, from its calories. However, protein as an energy source is not so efficient. The body has to work twice as hard to use protein for energy. The conversion of protein into glucose for energy requires two passes through the energy cycle. This causes our bodies to burn extra calories, simply from digestion. 

Thus when we eat protein, we use it for our muscles, and growth and repair. We also use it for energy but burn extra calories in doing so. Fat, however, is just a calorie dense food strictly used for energy and any excess gets quickly stored, as fat.

In conclusion, when wanting to lose weight and/or avoid weight gain, a person's diet should consist of lean protein, fruit, and vegetables, with minimal fats and minimal starch-like carbohydrates. This allows for your body to efficiently process all consumed items for necessary functions and leaves nothing left to store as fat.

Enas Shakkour
Nutrition & Dietetics

Fat has 9 calories per gram. Protein has 4 calories per gram. Because fat is so calorically dense, a high-fat diet usually results in the consumption of too many calories. When one consumes more calories than their body burns, weight gain results. One should try to consume about 30% of calories from fat, and about 20% of calories from protein. Remember to choose your fats wisely as well.

Sarah Mathot
Nutrition & Dietetics

Weight gain is a result of consuming more calories than what is expended over a period of time. If a diet is "high" or more than what an individual needs from protein or fat than weight gain will be the result. Fat provides our bodies with more calories per gram than protein therefore it would be easier to consume excess calories from fat.

Rebecca S. Reeves
Nutrition & Dietetics
Three published studies (2 one year studies and 1 two year study) have now demonstrated that any reduced calorie diet can produce clinically meaningful weight loss regardless of which nutrient is emphasized. What is most important is finding the calorie-reduced diet that fits your lifestyle and a diet that you feel comfortable in following for the long term. Most diet failures occur because a person cannot incorporate the new eating patterns into his/her lifestyle so that the weight loss is maintained.
Alberta Scruggs
Nutrition & Dietetics

The reason a high-fat diet causes more weight gain than a high protein diet is two-fold. A gram of fat has more kcalories, (more energy-dense), and uses a lessor amount of kcalories to convert and store dietary fat as fat in the body than protein does.

  1. One gram of fat provides nine (9) kcalories. One gram of protein provides 4 kcalories. If you eat 70 grams of fat, you eat 630 kcalories. If you eat 70 grams of protein, you eat 280 kcalories (more than twice the amount).
  2. It requires more energy to convert protein to usuable substances for the body (amino acids, glucose), to eliminate unusable substances (ammonia), or to be converted and stored as fat in a fat cell; whereas, it takes a small amount of energy (about 3% of total fat kcalorie amount), to store dietary fat in fat cells (because it's already fat).
Louise Goldberg
Nutrition & Dietetics

Gram for gram, fat is more than double the calories as protein. If you consume a high fat diet, you are more likely to consume a higher amount of calories. Those excess calories get stored as fat and increase your weight. It is best to consume a diet that includes lean proteins and a small amount of HEALTHY fats, such as lean meats, fish, poultry, beans, soy products and nuts.

Molly Morgan
Nutrition & Dietetics
The bottom-line of weight is calories in versus calories out. High fat foods likely are providing more total calories (1 gram of fat has 9 calories) than high protein foods (1 gram of protein has 4 calories). Additionally, the key to maintaining weight loss is the ability to adhere to the plan, with whatever works best for your taste preference and lifestyle!
Meagan Mohammadione
Nutrition & Dietetics

I agree with everyone else when they say that eating more fat leads to eating more calories. 

Another reason that a high-fat vs. high-protein diet leads to weight gain is that protein is more "filling" than fat. Protein is harder for our bodies to breakdown, so it stays in our stomach longer, keeping us feeling full.

Bonus: Eating protein causes a little jump in our metabolism while our bodies work to digest it!

This doesn't mean that we should avoid fat completely! A moderate amount of fat in our diet is necessary for absorption of Vitamins A, D, E, and K. People who eat very little fat are actually at risk for developing deficiencies of these important vitamins!


Katherine Sanchez
Nutrition & Dietetics
Eating a high-fat diet may or may not cause weight gain than a high-protein diet. Weight gain happens when the food you eat has more calories than your body is burning. If you're eating too much food, you're going to gain weight, regardless. High-fat diets have gotten a bad rap, but the truth is that we NEED to eat good fats (think: avocados, nuts, seeds, salmon, tuna). Our cell membranes are made from fats, our brains need good fats, and without fat in our diet, we can't absorb vitamins A, D, E or K. Studies published in the International Journal of Obesity (2003) and the Journal of the American College of Nutrition (2011) have shown that people who eat certain foods that are high in fat (pistachios and almonds, for example) are actually more likely to maintain a healthy weight than those who don't. So does that mean you should eat lots of fatty foods? No, but don't shun them, either. Moderation is the key word for weight loss, along with reducing calories (from all sources), exercising regularly, and getting at least 6-8 hours of sleep every night. 
Rebecca Scritchfield
Nutrition & Dietetics
A high fat diet would cause more weight gain if the total energy intake over time exceeded your energy expended (the old calories in vs. calories out). Protein and fat are both nutrients that provide "sustained" energy. However, fat has 9 calories per gram (energy dense) and protein only has 4 calories per gram. You want to strike a balance with carbs, protein, and fat. Your eating pattern can resemble a "higher" percentage of fat than protein. For example, if you put together a plate with a fist size of whole grain, 2 fists of veggies, a palm size amount of protein and one source of fat (avocado, olive oil for example). This may provide about 50% of calories from carbs, 20% from protein and 30% from fat.
Cindy Guirino
Nutrition & Dietetics

High fat foods usually come in a package with high sugar foods - think Cupcake!

These foods can really pack on the pounds plus they create an addictive like pattern in the brain which has you craving more fat and sugar bombs of calories which can eventually lead to weight gain. Eat more whole foods and eat foods that have natural fat in them like nuts to avoid weight gain.

Nadine Pazder
Nutrition & Dietetics
Because there is a difference in the amount of energy (calories) provided in protein, carbohydrate and fat. Both protein and carbohydrate provide 4 calories per gram. Fat provides 9 calories per gram. And because fat provides a lot of calories in a small serving, it is much easier to gain weight by adding fat to your diet.
Hiral Modi
Nutrition & Dietetics

Fat is denser in calorie than protein. 1 gram of Fat = 9 kcalories while 1 gram of Protein = 4 kcalories. So when you eat high fat diet you are consuming more calories as compare to equal amount of high protein diet. Thus it leads to weight gain. In addition body stores fat and burns fat only when it needs energy for example during exercise. On the contrary high protein diet helps to build muscle and muscular body requires more energy.

For each extra pound of muscle body burns 50 additional calories just for maintenance. Moreover, body burns more calories (almost twice) to digest protein as compare to fat. Also, protein helps to increase satiety (feeling of fullness after you eat) more than the fat, so after high protein meal you feel full for longer time and less likely to consume unnecessary calories.

Continue Learning about Nutrition and Weight Loss

Burn More Calories with This Sandwich Choice
Burn More Calories with This Sandwich Choice
Energy used for digestion accounts for a good chunk of your daily calorie burn. And you can boost that burn even higher just by choosing whole-grain b...
Read More
What foods can I eat a lot of if I want to lose weight?
F. Michael Gloth, IIIF. Michael Gloth, III
Some foods -- such as celery -- can be eaten without much concern about weight gain. These foods are...
More Answers
6 Low-Calorie Foods To Buy at Trader Joe's
6 Low-Calorie Foods To Buy at Trader Joe's6 Low-Calorie Foods To Buy at Trader Joe's6 Low-Calorie Foods To Buy at Trader Joe's6 Low-Calorie Foods To Buy at Trader Joe's
Cauliflower pizza crust and other prepackaged foods that won’t blow your diet.
Start Slideshow
What Is a Superfood?
What Is a Superfood?

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.