What Makes You Fat: Carbs or Calories?

Nutrition information seems to constantly contradict itself. Some professionals insist that high-fat diets make you fat. Others insist that the problem is carbohydrates and not fat. A third opinion is that it doesn't really matter whether you're eating high carbs or high fat: The number of calories you eat determines how much fat you gain.

There are many diet plans out there; the key is to be consistent with one. (Image: Floortje/E+/GettyImages)

Tip

Ultimately the number of calories you eat during the day is what makes you fat.

Famous Low-Carb Diets

There are numerous low-carb diets that have continuously grown in popularity. Keto and Atkins are two well-known low-carb diets. They're both based on lowering carb intake and boosting fat. Both diets have a large following, and some people swear by them. Since you can lose weight on low-carb diets, there must be something to them.

The rationale for low-carb diets often revolves around insulin. When your blood sugar levels go up, your body secretes insulin to pull sugar out of your blood stream and store it as fat. Eating high-carb meals or sugary food makes your insulin levels go up, so it should make sense that lowering carb intake would decrease the amount of fat you store.

Well-Known Low-Fat Diets

On the other hand, low-fat diets like DASH, which stands for Dietary Approach to Stop Hypertension, advocate for lowering fat. Saturated fat in particular has been the subject of much scrutiny in the world of heart health and obesity. There's evidence that eating a diet high in saturated fat increases your risk for heart disease.

According to an article from the U.S. Department of Agriculture, fat has 9 calories per gram, compared to carbohydrates and protein, which both have 4 calories per gram. Since fat has over twice the number of calories by weight of carbs and fat, it makes sense that some people try to avoid it.

Calorie Counting Method

Another solution to weight loss is more straightforward: worry about calories in vs. calories out. Calorie counting used to be a very popular method of dieting, and while it can make you obsessive, it can also be very helpful.

Throughout the day your body is constantly burning and storing fat. When you want to lose fat, your goal is to get your body to burn more fat than it stores. This is called a negative energy balance. In other words, you're burning more calories than you take in.

This approach seems simple, but works for many people. The only way to truly settle the dispute about calories vs. carbs is to use the scientific method. Researchers have to test the hypothesis and come to a conclusion.

Cross-Sectional Survey Studies

Keep in mind when reading any diet study that not all studies are created equal. Many diet studies are cross-sectional survey studies, which means that researchers follow and observe a person's diet over a period of time by checking in with them. They collect data and try to come up with an answer from the results. An example of this kind of study is the census.

While these studies are cheaper and easier to conduct, they're not very accurate. At best they can prove that two things are associated, such as carb intake and weight gain. However, these studies can't prove that one thing causes another.

Experiments are helpful because they allow scientists to change things. For example, they can have someone eat a high-carb diet for a few weeks then eat a low-carb diet. If the calories stay the same and they don't lose any weight, then you know that the number of carbohydrates they eat per day isn't what determines weight loss.

Experimental and Controlled Studies

Experimental studies are more difficult for the subject and more expensive for the researchers, so they usually use fewer people. The time period is usually shorter than a survey.

Studies where researchers have subjects report the food they're eating are often inaccurate because it's difficult to correctly measure all the food you eat. That's why researchers found that most people inaccurately report their food intake during diet studies.

What Research Shows

To study whether cutting carbs or cutting calories makes you lose weight, you need a well-controlled study. During the study, the subjects have to eat the same number of carbs in both the low-fat and low-carb group. If they only have to cut carbs but can eat as many calories as they want, calorie intake could still be the culprit.

A well-formed study, published in the Journal of Obesity & Weight Loss Therapy in 2015 showed that, as long as calories were the same, it didn't matter what diet the subjects were on. They lost an equal amount of weight between the low-fat and low-carb groups. This study shows that calories are the most important thing.

The Twinkie Diet

A prime example of the importance of calories is the Twinkie diet. One man decided to eat a diet of processed foods for a few weeks but monitored his calorie intake. He kept his calorie intake low enough that he would be in a negative energy balance.

Over the course of the diet he lost weight, even though he kept sugary and processed carbs in his diet. While it's not a proper scientific study, the Twinkie diet is an example of how weight loss truly works: The thing that matters most is calories in versus calories out.

Insulin and Fat Storage

The argument that carbs make you fat because of increased insulin doesn't make much sense. The problem is that other, non-carbohydrate foods can make your insulin spike. Whey protein, when added to a meal, caused double the amount of insulin to be released.

Find What Works for You

In the end, the most important thing is that you can stick to your diet. While calories are the most important thing, if cutting out carbs makes it easier to lower your calories then low-carb is best for you.

You can run this experiment on yourself by downloading a diet tracker app like MyPlate. With this app you can input the food you ate and it will break down the number of calories you consumed and what percentage of it came from protein, fat and carbs.

Play around with your diet and lower carbs for one week, then lower fat the next while keeping calories the same. See which one you like better and how easy each style of diet is to follow.

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