Does Eating Fat Make You Fat? What Research Says
Americans have long been obsessed with losing weight. According to historians, the notion of dieting to lose weight in American stretches back more than 150 years. Over time, the idea of the best way to drop pounds has changed considerably.
In the 1960’s, doctors began to tout a low fat diet as good for everyone – not just high-risk heart patients. By the 1980’s, the low fat approach to dieting became the most prominent ideology in the United States, promoted by the health media, physicians, and even the federal government (remember the food pyramid?). As researchers began to study nutrition more closely, however, they learned that low fat diets aren’t best for everyone – and that the sugar that was pumped into our foods to compensate for lack of fat was making us even fatter.
While it may seem counterintuitive, particularly for those of us who grew up on low fat being the ideal, eating fat does not make you fat. Instead, including fat as part of your diet – particularly healthy fats – can actually help you to lose weight. Below, we break down the science that proves that eating fat does not cause you to gain weight.
Why Eating Fat Does Not Make You Fat
In the United States, we use the word “fat” for two different kinds of fat: fat in foods as well as body fat. To understand why eating fat does not make you fat, it is important to understand the distinction between these two types of fat.
Our bodies store fat in adipose tissue. These fat cells are essential for our survival, as they are used as an energy source and to build cell membranes as well as the sheaths that surround nerves. Without any source of fat, our bodies cannot function properly.
When we cut too much fat from our bodies, it can result in health complications. A 2013 study of a competitive bodybuilder found that when he reduced his body fat percentage from 14.8% to 4.5% over time, his overall health suffered. Researchers observed that this man had reduced levels of testosterone, higher levels of cortisol (the stress hormone), altered mood status, reduced immune function, and a decreased ability to perform physically.
This study demonstrates that we need fat in our bodies. When we cut too much fat, it can actually be detrimental to our health.
Dietary fat includes any type of fat that we consume in our foods. These fats – and specifically the fatty acids that they contain – help our bodies absorb some vitamins and minerals. They are also vital for a range of functions in our bodies, including blood clotting, inflammation, and muscle movement. Because our bodies cannot produce all of the fatty acids that it needs on its own, we must consume fat to provide these fats.
Along with protein and carbohydrates, dietary fat is one of three macronutrients that provide the energy that we need to survive. Each type of macronutrient contains calories, or units of energy. While protein and carbohydrates have 4 calories per gram, fat has 9 calories per gram.
In a laboratory, all calories are the same and are burned equally. However, our bodies are not laboratories – they are incredibly complex. While it may seem odd, eating fat actually helps us lose weight because it helps to shut off our brain’s hunger and craving centers. According to a study performed by the National Institutes of Health (NIH), people who ate more fat burned over 100 calories more each day compared to people who ate an identical amount of carbs. Over the course of a year, burning 100 extra calories a day amounts to a 10 pound weight loss – without any special diet or additional exercise.
By contrast, eating a lot of carbohydrates can actually make you hungrier, causing you to eat more (and gain weight). In a 2013 study, researchers from Harvard Medical School and Boston Children’s Hospital gauged the metabolic response of participants after eating a high carb/low fat versus a high fat/low carb meal. Four hours after eating a high carbohydrate meal, participants had lower blood glucose levels and said that they felt hungrier than those who ate the higher fat meal. This physiological response to carbohydrates leads to both increased hunger and cravings, particularly for higher carb foods – which causes weight gain. Similar studies have reached the same conclusion.
The upshot? The old saying that a calorie is a calorie simply isn’t true. Some calories – particularly those that come from carbohydrates – promote weight gain. Other calories (such as those that come from dietary fat) can help you feel satiated and are associated with weight loss.
Of course, eating too many calories – no matter the source – will cause you to gain weight. However, if your diet is high in carbohydrates and low in fat, you are more likely to consume too many calories. If you are trying to lose weight, dietary fat isn’t the enemy – and may even be the key to eating less and getting into a calorie deficit.
Good Fats Versus Bad Fats
Not all fats are created equal. Certain types of fats are better for you than others, and can actually promote heart health. For this reason, when you are adding fats to your diet, it is important that you focus on the right types of fats.
There are four types of fats that you may consume in your diet:
- Monounsaturated fat: found in a variety of foods and oils, such as nuts, vegetable oils, peanut and almond butter, and avocado.
- Polyunsaturated fat: most often found in plant-based foods and oils as well as fish, such as tofu, seeds, walnuts, roasted soybeans, soft margarine, chia seeds, flax seeds, salmon, sardines, and trout.
- Saturated fat: found in high fat meats and dairy products, such as fatty cuts of beef, pork and lamb, dark chicken meat and skin, whole milk, sour cream, tropical oils, and lard.
- Trans fat (trans fatty acids): found in foods that contain partially hydrogenated vegetable oils, such as fried foods, baked goods, processed snack foods, margarine, and vegetable shortening.
Generally, you should focus on polyunsaturated fats (PUFAs), monounsaturated fats (MUFAs), and saturated fats, with an emphasis on unsaturated fats (PUFAs and MUFAs). These types of fats are associated with a lower risk of heart disease and will help you feel full. Saturated fats can also help you feel full and may also lower the likelihood of cardiovascular disease.
At the same time, try to avoid trans fats, or manufactured fats. Manufacturers make these fats by pumping hydrogen molecules into vegetable oils, which creates a more shelf-stable food – but is associated with a lot of health issues. Eating trans fats increases our risk for heart disease, causes inflammation, and may be linked to type 2 diabetes. If you see the words “hydrogenated” or “partially hydrogenated” on a list of ingredients, steer clear.
When adding fats to your diet, stick to ones that are naturally-occurring – such as those that are found in plant and animal products – and avoid fats from processed foods. In this way, you’ll reap the benefits of fat when it comes to weight loss and heart health, and avoid the health risks of trans fats.
Should I Buy Low Fat or Fat Free Foods?
When losing weight, it can be hard to break old habits. Many of us believe that low fat or fat free foods are healthier than foods that are high in fat. In reality, as demonstrated above, eating low fat, high carb foods can actually cause us to gain weight.
Manufacturers often pump low fat or fat free foods full of sugar to make up for the fat that they removed. As we know, eating sugar fuels cravings for more sugar, which often leads to weight gain.
At the same time, unless they are whole foods like a fruit or vegetable, low fat or fat free foods typically do not contain nutrients that our bodies need. By comparison, foods that contain healthy fats usually have plenty of vitamins and minerals. For example, ½ of a medium avocado contains 130 calories and 12 grams of total fat (mostly monounsaturated fats). They are also a good source of dietary fiber, phytochemicals, vitamin A, vitamin K, vitamin C, vitamin E, iron, potassium, zinc and calcium. By contrast, you can eat 130 calories worth of fat-free pretzels – and get none of those beneficial vitamins, minerals, or fats.
While calories still matter when it comes to weight loss, the type of food that we eat may be even more important. Ultimately, by focusing on whole foods and healthy fats, you can improve your overall health and shed excess pounds.
Lose Weight in a Healthy and Sustainable Way with Ideal You
Millions of Americans struggle to maintain a healthy weight. A low fat diet may seem like a good way to drop pounds, but we know that diets don’t work – and that eating fat does not make you fat. Instead, including healthy fats can actually help you lose weight.
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