Why does dietary fat cause weight gain?

Judy Caplan
Nutrition & Dietetics
Dietary fat does not necessarily cause weight gain. The amount of fat and the type of fat will determine if you gain weight as will your total daily calorie intake. We need healthy fats to maintain a healthy heart, for optimal brain function, and for satiety. Healthy fat in limited amounts actually helps you lose weight in conjunction with an overall calorie controlled diet.
Pierre Dukan
Nutrition & Dietetics

Fats are the enemy of anyone trying to be slim, as they represent the most concentrated form in which surplus energy is stored. Eating fats means you are eating an animal’s energy reserves. There are 2 major sources of fats: animal and vegetable.

Animal fat, found in a virtually pure state in lard, is very much present in products such as pâtés, salamis, sausages, hot dogs etc. Grass Fed Beef is not as fatty, especially cuts that can be grilled. Only ribs & the rib eye are really rich in fat. Butter is practically a pure fat. The fat content of heavy cream is around 36%.The 5 fish fattiest fish are sardines, tuna, salmon, mackerel, & herring. These fish are no fattier than ordinary steak & coldwater fish is rich in omega 3 fatty acids, known to protect against cardiovascular disease.

Vegetable fats for the most part, represented by the long list of plant & nut oils & fruits such as avocado. Oil is even fattier than butter. Although some oils like olive, walnut or grape seed oils have nutritional qualities that have been proved to protect the heart & arteries, they all have the same caloric value & should be removed from any weight loss diet, especially during the first 3 phases of my diet and eaten sparingly during the final Stabilization phase.

Those wanting to be slim, & in particular for those who are trying to lose weight, fats represent every danger possible. Fats contain, by far, the most calories—9 calories per gram (more than double the calories in carbohydrates, which provide only 4 calories per gram). Fats are very rich foods and so are rarely eaten alone. Oil, butter, and heavy cream are often associated with bread, starch, pasta, or salad dressings; the combination increases the overall calorie count considerably. Fats are not assimilated as quickly as fast sugars, but are assimilated far more quickly than proteins, thus their comparative energy contribution increases accordingly. Fatty foods reduce our appetite moderately, & snacking on them, rather than proteins, does not reduce your desire for a large meal afterward or delay your hunger. Finally, animal fats with high amounts of fatty acids— butter, sausages, dried meats & fatty cheeses— pose a potential threat to the heart. For this reason, they can't be consumed without restriction, as has been the case with other high protein diets.

For more information on my diet go to

Jessica Crandall
Nutrition & Dietetics
Fat yields the most calories per gram at 9 calories, more so than any other macronutrient (such as carbohydrates and proteins which yield 4). Fat typically is included in most food choices, so it becomes really easy to over eat fat. Extra fat that is not needed for the body to function is then stored in the body leading to weight gain.
Sarah Worden
Nutrition & Dietetics

Fat is higher in calories per gram than the other 2 macronutrients (Carbohydrates = 4 calories per gram, Protein = 4 calories per gram, Fat = 9 calories per gram). So, a smaller portion of a food high in fat generally packs more calories than the same size portion of a food that is primarily made up of carbohydrates or protein. Don't avoid fat completely, just watch portion sizes if you are watching your weight. Also, the kind of fat matters as well. Plant based fats (olive oil, nuts, avocado) generally provide more nutritional benefits than animal based fats (cheese, cream, beef).

Enas Shakkour
Nutrition & Dietetics
Dietary fat does not necessarily cause weight gain. Our bodies actually need some fats. Those are called essential fatty acids. There are fats, however, that are not essential, and only contribute excess calories to one's diet. The consumption of more calories than one burns causes weight gain. Because dietary fat is very "calorie-concentrated", excessive consumption of fat may result in excess calorie consumption. Dietary fat in moderation should be a part of a healthy diet.
Nadine Pazder
Nutrition & Dietetics

You will gain weight whenever you are ingesting more calories through food than you expend in exercise. At 9 calories per gram, fat contributes more calories to your diet faster than either protein or carbohydrate. As a very practical example, 2 pats of butter contain more calories than the baked potato that you will put it on.

When you are looking for strategies to manage your weight, keeping a food diary and monitoring your fat intake is a good first step. But the fact remains that we need some fat daily to stay healthy. Schedule a visit with a Registered Dietitian to develop a meal plan that meets your specific needs.

Marilyn Ricci, M.S., R.D.
Nutrition & Dietetics

Fat is the most concentrated form of calories. It is easy to eat too much fat because it tastes good. It is what makes meat, chips, fries, ice cream, etc. taste extra good. However, a little fat can go a long way. For example, reduce the amount of mayo or butter you put on bread. It will still taste good, but with a lot less calories. Limit high fat snack foods. They are empty calories, anyway. 

Michaela Ballmann
Nutrition & Dietetics

The main reason that dietary fat may promote weight gain is because it is more Calorically-dense than protein or carbohydrates. Both protein and carbs have 4 Calories per gram, but fat has 9 Calories per gram (2.25 times more!). So, if you tend to eat a lot of high-fat foods, you are also eating a lot of Calories in a small amount (weight or volume) of food. If you were to replace the fat with a nutrient-dense food, such as vegetables, a broth-based soup, or fresh fruit, you could eat a much greater volume of food for the same or an even fewer amount of Calories.

Too many calories -- whether they come from carbohydrate, protein or fat -- get stored as body fat. Of the three macronutrients, fat has the most calories per gram at 9. Carbohydrate and protein each contain 4 calories per gram. That’s why 1 tablespoon of table sugar (all carbohydrate) that weighs 12 grams has about 45 calories, and 1 tablespoon of corn oil (all fat) that weighs 14 grams has about 125 calories.

Most health organizations in the United States recommends limiting total fat intake to less than 35% of total calories, with no more than 10% of fat coming from saturated fats. The majority of fat intake should be derived from monounsaturated sources such as olive and canola oils, olives, avocados, nuts, and nut products, as well as fish that are sources of omega-3 fats.

Weight Watchers offers a comprehensive approach to weight loss that can help you reach your goals.
Jamie Johnson
Nutrition & Dietetics

Weight gain is a product of consuming more energy (calories) through food & beverages than you expend through the combination of what it takes to sustain the very basic functions of life (resting metabolism), metabolizing the food you ingest (thermic effect of food), and what you burn in daily activities (exercise + daily activities) also known as your exercise metabolic rate. A person can gain weight anytime he or she consumes more calories than needed to fuel these 3 things, (regardless of if they come from dietary fat, carbohydrates, protein, alcohol, or a mixture of these nutrients).

The reason fat is often blamed for weight gain is because every gram of fat contributes 9 kilocalories of energy, while sources of either carbohydrate or protein contribute only 4 kilocalories of energy per gram. Fat is more calorically dense, so it adds up quicker in the calorie department. 

Remember there are different types of fat and some is better than others. We need fat in our diets for many reasons; however, it is recommended that no more than 30% of your total daily caloric intake comes from dietary fat. Of that 30%, no more than 7-10% should be from saturated fat, as it has been associated with many negative health risks. Consuming too many carbohydrates or protein can also lead to weight gain because amounts beyond what the body needs will simply be stored as fat. 

Laura Motosko, MSEd, RD
Nutrition & Dietetics

Fat is one of three macronutrients, including carbohydrate and protein. A gram of fat is about 9 calories, as compared to 4 calories per gram for carbohydrate and protein. Dietary fat has greater energy density in foods and may cause weight gain if it is consumed in an excess amount than the energy you expend in physical activity.

Jim White
Nutrition & Dietetics

It is important to include fat in the diet, however people eating a lot of high fat foods will gain weight. When looking at total consumption for the day, generally keeping fat intake to 30% will be a good balance for weight maintenance. When trying to lose weight staying between 20% & 25% fat intake will help keep the calories down. 

It is also important to choose most of your fats from the mono & poly-unsaturated fats. These "healthy fats" are the plant based fats, such as nuts, olive oil, avocado, peanut butter, etc. Saturated fats should be limited, these "unhealthy fats" are the animal-based fats that are found in meats, butter, cheese, & dairy that is not fat-free. Transfat should be avoided entirely.

Alberta Scruggs
Nutrition & Dietetics

One reason why fat has the tendency to cause weight gain is we eat more of it because it flavors food and makes it taste delicious.

But on a more clinical note I can think of two reasons:

  • Dietary fat provides more than twice the amount of kcalories (9 kcalories) than carbohydrate (4 kcalories) or protein (4 kcalories) does.
  • It doesn't take as much energy (about 3%), to convert and store dietary fat as it does to convert and store glucose or protein. Fat is already fat. All it has to do is move into the cell.
Eric Olsen
Dietary fat is the most densely caloric food -- nine calories per gram (more than twice the calories in a gram of carbohydrates or protein). Thus, the more fat in your food, the more likely you are to take in more calories than you should. Fats are quickly and easily stored by the body, so most of the fat in your food tends to go directly to the waistline.
Lifefit: An Effective Exercise Program for Optimal Health and a Longer Life

More About this Book

Lifefit: An Effective Exercise Program for Optimal Health and a Longer Life

An easy-to-follow programme for lengthening and improving lives. More than an exercise guide, this text is an effective tool for making meaningful lifestyle decisions to benefit long-term fitness. In...

Continue Learning about Fats and Weight Loss

Lose Weight by Adding the Right Fat
Lose Weight by Adding the Right Fat
Former San Diego Charger’s lineman Nick Hardwick retired from the National Football League and from his daily 5,000-plus calorie diet that included sa...
Read More
How can a low-fat, high-carbohydrate diet keep me from losing weight?
Marilyn Ricci, M.S., R.D.Marilyn Ricci, M.S., R.D.
A high carbohydrate, low fat diet will only help you lose weight if your carbohydrates are high fibe...
More Answers
What types of fats should I avoid if I want to lose weight?
Ozgen DoganOzgen Dogan
Stay away from saturated fats (found mostly in foods from animals and some plants), like butter,...
More Answers
Is Diet or Exercise More Important for Weight Loss?
Is Diet or Exercise More Important for Weight Loss?

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.