Low-carb or low-fat: Which is healthier?

By Connie Capone
Published August 12, 2020

Key Takeaways

Over the years we’ve seen countless diet fads come and go, each one promising to help us shed unwanted pounds with ease, but many of these get-thin-quick diets are like get-rich-quick schemes—they tend to help us lose dollars quicker than weight.

On the other hand, low-carb and low-fat diets with names you might recognize, like Atkins, Keto, Jenny Craig, and Paleo, have demonstrated staying power among all the fleeting fads. They also come with tons of supporters and naysayers—many of them paid spokespeople—so it can be tough to find a trustworthy voice when searching for the dietary approach that’s right for you.

Let’s take a look at the differences between low-carb and low-fat diets to help you decide which is better for weight loss and improved health.

Fats and carbs: the good and the bad

Fats, carbohydrates, and proteins make up the trio of macronutrients, which the body requires to function properly. Dietary fats support cell growth, protect organs, and absorb some nutrients, among other tasks. Carbohydrates act as the main source of energy, after being broken down by the body into simple sugars. Dietary proteins supply essential amino acids, which support protein synthesis and promote the growth and repair of tissue.

These macronutrients—especially fats and carbohydrates—have gained differing reputations among dieters because different types of fats and carbohydrates provide different nutritional value to our bodies.

Fats, for example, often get a bad rap, but only two of the four major types of dietary fats are associated with health issues. Saturated and trans fats raise LDL cholesterol and are linked to heart disease and stroke when consumed in high quantities. Monounsaturated and polyunsaturated fats lower bad cholesterol. Experts generally recommend replacing the “bad fats” with the “good fats.”

Carbohydrates are also often vilified by dieting gurus. But again, it depends on which type you choose. Carbohydrates are either simple or complex, depending on the food’s chemical structure and how quickly the sugar is digested. Simple carbohydrates, often found in processed foods like soda and breakfast cereal due to ingredients like sugar and high-fructose corn syrup, are digested quickly. They provide little nutritional value and are associated with weight gain, coronary heart disease, diabetes, and fatty liver. Complex carbohydrates, on the other hand, are digested more slowly and do not spike blood sugar the way simple carbohydrates do. They can be found in foods like fruits and veggies, nuts, beans, and whole grains.

How the diets work

Low-fat diets allow foods in which 30% or less of the total calories come from fat (think egg whites, whole grain cereals, skinless chicken breast, and low-fat dairy). Because fat contains 9 calories per gram and carbohydrates contain 4 calories per gram, it’s theoretically more advantageous from a caloric standpoint to consume more complex carbohydrate-based foods while limiting fats. Jenny Craig is a popular low-fat diet that achieves its aims through portion control, limiting users to low-fat, low-calorie meals.

Low-carb diets restrict overall consumption of carbohydrates to varying degrees, ranging from a moderate intake of carbohydrates (defined as 26% to 44% of total calories) to a very low intake (less than 10% of total calories). Examples of low-carb foods are fish, meat, cheese, oils, eggs, and leafy green vegetables. The philosophy behind this diet is that by lowering the insulin response in the body—which enables fat-storage—weight loss will ensue.

The popular keto diet is a version of the very low-carb approach, which propels the body into a metabolic state called “ketosis” when there is low carbohydrate availability in body tissues. During this state, fats are converted into ketones, which fuel the body in place of carbohydrates, accelerating weight loss.

Low-carb vs low-fat

When it comes to weight loss, some studies found no considerable advantage in choosing a low-carb vs a low-fat diet. A meta-analysis published in the American Journal of Epidemiology analyzed data from 23 trials comparing participants who followed a low-carb with those who followed a low-fat diet. Researchers found that both diets were equally effective at reducing body weight and both diets reduced participants’ blood pressures, LDL cholesterol, and blood glucose.

These findings were supported in a clinical trial, published in JAMA, by researchers at Stanford University School of Medicine. The researchers randomly assigned just over 600 participants to either a low-carb or a low-fat diet. After 12 months, the researchers found no significant difference in weight loss between the two diet groups.

However, low-carb diets were associated with faster fat loss, according to a study published in Nutrition & Metabolism. Researchers assigned 28 participants to either a very low-carbohydrate or low-fat diet and found that the low-carb dieters saw better short-term weight and fat loss over a 2-month period.

One advantage of low-carb diets may be that they are more effective at reducing hunger because protein (a key source of nutrition in most low-carb diets) is, calorie-for-calorie, more satiating than carbohydrates or fat. A study published in Nutrition Journal evaluated how different snacks affected appetite. Compared with high-fat snacks, high-protein snacks improved appetite control, satiety, and reduced subsequent eating.

Both diets have their fair share of shortfalls, too. The low-fat trend has become confusing for some dieters, as so-called healthy products touted as “low-fat” could be loaded with sugar or other processed additives. In addition, many are confused by the types of fats they should be eating. For the first time in 40 years, the Dietary Guidelines for Americans—released jointly by the US Department of Agriculture and the Department of Health and Human Services—will likely remove any recommendations against total fat consumption when the guidelines are updated at the end of 2020. Reportedly, this is due to a lack of evidence that total fat intake is associated with direct harms, since “total” includes unsaturated fats, like nuts and fish, which have proven dietary benefits.

The American Heart Association has warned against the pitfalls of low-carb diets, issuing a statement against the high-protein, high-fat, low-carb approach, claiming that people who follow such diets may suffer from insufficient vitamin and mineral intake and put themselves at risk for cardiac, renal, bone and liver abnormalities.

Which diet is better?

Both low-carb and low-fat diets can be beneficial for people pursuing weight loss and improved health, but carbs and fats are simply nutrients that make up foods—the quality of the food itself is the most important factor for overall health. Complex carbohydrates such as legumes, starchy vegetables, and whole-grain foods should be embraced (in moderation, of course). Likewise, healthy fats from foods like avocados, olive oil, nuts and seeds help fight fatigue, boost brain power, and control weight.

Rather than choosing one strict diet over another (where failure rates—and disappointment—tend to be high), think about embracing a strategy that allows you to swap simple carbohydrates for complex carbohydrates and replace “bad fats” with “good” ones. And remember not to be distracted by fads—while a low-carb diet may bring quicker short-term weight loss, a diet must be enjoyable in order to be sustainable. The best bet is to take pieces of wisdom from both diets, implement them in your routine, make them a habit, and then move out of the diet mindset altogether.

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