Low-Carb vs. Low-Fat: Which is better for weight loss?

With so many diet and nutrition tips floating around it can be difficult to know what to choose from. From low-fat to low-carb, high-protein to keto to paleo, it seems there are a plethora of options to choose from if you have a goal of weight loss, making decisions more confusing than ever. So, let’s look at the research in order to answer the debate of low-carb vs. low-fat: which is better for weight loss?

For years, experts have debated which diet is best for weight loss: low-carb or low-fat? If you want to lose weight, is it better to go low-carb and cut out pasta, crackers, and bread, or go low-fat and cut out butter, nuts, and cheese? Well, as it turns out, both low-carb diets and low-fat diets are equally effective for weight loss.

What is a Low-Carb Diet?

A low-carb diet, or a carb-restricted diet, is a diet in which the total calories from carbohydrates are low relative to protein and fat. A low-carb diet is one that restricts carbohydrate-rich foods, specifically sugar, grains, and starch-rich foods (bread, pasta, potatoes) and focuses on carbohydrate-based foods that are low in carbohydrate density (vegetables and fruit). A low-carb diet is by nature higher in protein, fat, and vegetables.

What is a Low-Fat Diet?

A low-fat diet, or a fat-restricted diet, is a diet in which the total calories from fat are low relative to carbohydrates and protein. A low-fat diet is limited in sources of fat (animal fats, oils, butter, avocado, nuts, seeds) and focuses on low-fat whole foods (whole grains, legumes, lean meats, fruits, vegetables) and/or low-fat food products (0% milk, low-fat yogurt, light dressings). A low-fat diet is by nature higher in protein and carbohydrates.

What is Needed for Weight Loss?

At the foundational level, weight loss is based on an exchange of energy. In order for weight to be lost, there must be a deficit of energy, more specifically; calories expended must be greater than the calories consumed. The amount of energy burned (or calories burned) is dependent on a number of controllable and noncontrollable factors including age, weight, sex, activity level, and exercise, while energy consumed (or calories consumed) is dependent on the amount of food and drink a person consumes. It is important to understand that there are many factors that play a role in weight loss, however, the one essential requirement for weight loss to occur is a calorie deficit.

This calorie deficit can be created in a number of different ways, or a combination of different ways, such as increasing activity levels, reducing portion sizes, and/or tracking calories to reduce overall calorie intake. In addition to these methods, some diets will advocate for limiting or restricting a specific macronutrient, such as carbohydrates or fats, in order to support total calorie reduction. Reducing carbohydrate intake, as is done in a low-carb diet, or reducing fat intake, as is done in a low-fat diet, can be viewed as tools to reduce total calorie intake to help create the energy deficit needed for weight loss to occur.

Why Use Carbs and Fat for Weight Loss?

Both carbohydrates and fats are used as tools to reduce total energy intake in an effort to support the energy deficit needed for weight loss for a variety of different reasons.

Foremost, carbohydrates and fats are both sources of calories. Every 1 gram of carbohydrate consumed provides 4 calories of energy, while every 1 gram of fat consumed provides 9 calories of energy. Therefore, by reducing the number of carbohydrates or fat consumed in the diet you can quickly reduce the total number of calories consumed to create a calorie deficit. For example, in a low-carb diet, by removing 1/2 cup of oats (which contains 27 grams of carbohydrates) you are able to omit 150 calories. Alternatively, in a low-fat diet, by removing 30 grams of cheese (which contains 10 grams of fat) you are also able to omit 150 calories.

One of the reasons that low-fat diets have long been touted as the solution to weight loss is that they are a simple way to reduce calories quickly. Since fat is more calorie-dense than carbohydrates, 9 calories per gram as compared to 4 calories per gram, low-fat diets have been popularized for weight loss since even a small reduction in fat consumption can dramatically reduce total calorie intake.

Conversely, low-carb diets have also been touted as a solution to weight loss since some forms of carbohydrates, specifically highly processed carbohydrates, are dense sources of sugar and calories and, therefore, reducing their consumption can help to decrease total calorie intake. Moreover, refined carbohydrates have been shown to influence blood sugar and cause the pancreas to store excess energy as body fat, which has a negative impact on weight loss.

Although carbohydrates and fats are commonly used as tools to create this energy deficit, it should be noted that protein is rarely used since it is essential for muscle building, the efficiency of the metabolism, and balancing blood sugar, which have all been shown to support weight loss.

Low-Carb vs. Low-Fat: Which is Better for Weight Loss?

So, what is the best option for weight loss; low-carb or low-fat? The answer is that there is no one-size-fits-all solution, and it is important to understand that there can be flaws in both methods. In fact, a number of studies have shown that both low-carb diets and low-fat diets can support a weight loss goal when total calorie intake is controlled for. Most recently, a year-long study of 609 adults participants by Stanford University found that, when total calorie and protein intake were controlled for, a low-fat diet and a low-carb diet produced similar weight loss and improvements in metabolic health markers in participants. This study itself is notable due to its large group of participants, long duration, and careful monitoring of the participant’s diets, and contributes to a body of evidence that for weight loss neither low-carb or low-fat is superior when total calorie intake and protein intake is controlled for.

So, what does this mean?

Based on these findings, for a goal of weight loss, total energy (or calorie) intake is vital and if not controlled will impede the efficiency of both a low-carb and a low-fat diet.

For example, should someone opt to go the low-fat diet route and limit all sources of fat in their diet, they may find themselves less satiated and nourished given that fat is vital for cellular metabolism and cell signaling; the health of various body tissues; healthy hormone function; and essential nutrition absorption of fat-soluble vitamins A, D, E, and K. Should this occur, the individual may end up reaching for more carbohydrate-based foods in order to help fill the hunger void and this may, in turn, reduce the calorie deficit required for weight loss.

Alternatively, should someone choose to go the low-carb diet route, they may find themselves less satiated and nourished given that carbohydrates are used as the body’s primary source of energy. Should this occur, the individual may end up reaching for more fat-rich foods (nuts, avocado, cheese) in an effort to feel satiated, however, this can be detrimental to a goal of weight loss given fats are so calorie-dense, twice as calorie-dense as carbohydrates, which will reduce the calorie deficit required for weight loss.

However, as with all nutrition goals, it is important to understand that food quality always trumps quantity. Yes, how much you eat is important but the quality of the food that you eat is much more important than how much of it you are eating. Even if you are controlling for calories and consuming the “perfect” serving size of Oreos and Doritos, if you are not focusing on food quality you are likely missing the mark. Not only is focusing on food quality (i.e. real food) essential to ensure you are getting the nutrients, vitamins, and minerals required for optimal health but focusing on food quality can actually help to optimize how much you are eating at the same time. Processed or refined foods are designed to be hyper-palatable and highly addictive, making them easier to over-consume, while whole foods are nourishing, filling, and satiating. Think about it, when was the last time you ate a whole carton of eggs or a bag of boiled potatoes?

When it comes to weight loss, food quality is the foundational piece of the puzzle and how much you eat is also important. In order to support a goal of weight loss, real food must be consumed with a calorie deficit in mind, but how you choose to create a calorie deficit is completely up to you. Some people will do well monitoring portion sizes and calories across all macronutrient groups, while others may find limiting a specific macronutrient group, such as carbs or fats, a more effective approach to reducing their total calorie intake.

The Bottom Line

No matter what your health goal is, the best diet is always going to be the one that you are comfortable with and are going to follow consistently. Focusing on whole foods will always be the most important piece of the puzzle in order to ensure that you are getting the nutrients, vitamins, and minerals required for optimal health, and when it comes to weight loss, reducing calories by following a low-carb diet, a low-fat diet or simply monitoring total consumption across all macronutrient groups is completely dependent on the individual and what will work best for them.