Low Carb VS. Low Fat: What the Science Says

Low Carb VS. Low Fat: What the Science Says

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Low Carb VS. Low Fat: What the Science Says

Posted 2 years ago

Brian Stanton

Brian Stanton


SaVanna Shoemaker, MS, RDN, LD

SaVanna Shoemaker, MS, RDN, LD

Expert Approved

If you research low-carb vs. low-fat diets, you won’t find a consensus. Some sources demonize carbs, others demonize fat, and a brave few take a balanced approach.

The balanced approach is rare. Once someone forms a belief like “fat is bad for you,” they’re unlikely to change it. Cognitive dissonance, confirmation bias, and other quirks of psychology see to that.  

But there’s always room for a fresh, measured look at the evidence. Keep reading. By the end of this article, you’ll be in a good position to decide if either diet makes sense for you. 

What Is a Low-Carb Diet?

According to NIH StatPearls, a low-carbohydrate diet (low-carb diet) is a diet in which less than 26% of your calories come from carbohydrates.[*] The remaining calories come from protein and fat. 

Low-carb diets are best known for promoting weight loss. A large body of evidence supports this notion, and we’ll review some of it shortly.[*

The ketogenic diet (Keto diet) is the most researched low-carb diet. With carbs limited to 10% of daily calories, Keto is considered a “very low-carb diet.” 

On Keto, your macronutrient ratio is:

  • 55-75% fat calories
  • 15-35% protein calories
  • Under 10% carb calories 

Limiting carbs and increasing healthy fat consumption is the key to the Keto diet. Limiting carbs reduces blood sugar and insulin levels, which in turn stimulates fat oxidation and ketone production in the liver. This fat-burning metabolic state (called ketosis) may drive a variety of health benefits. 

What Is a Low-Fat Diet?

When you eat a low-fat diet, you consume less than 30% of your daily calories from fat.[*] The bulk of your calories come from carbohydrates and protein. 

Low-fat foods include lean meats, whole grains, egg whites, fruits, vegetables, low-fat dairy, and beans. If it has fewer than 3 grams of fat per 100 calories, it generally fits the bill. 

Why are low-fat diets popular? Mostly because they’re thought to be:

  1. Good for weight loss 
  2. Good for your heart 

We’ll cover weight loss in a moment. Let’s talk about reason number two. 

The hypothesis is that too much dietary fat increases heart disease risk by increasing serum cholesterol levels. It’s true, diets high in saturated fats have been shown to have this effect.[*

But even with saturated fat, the connection to heart disease is far from clear. In fact, multiple large meta-analyses (following about 1 million people) have found no link between saturated fat consumption and heart disease risk.[*][*

Low-Carb vs. Low-Fat for Weight Loss

If you want to lose weight, should you limit carbs or fat? Let’s see what the evidence says. 

We could go paper by paper. But there are dozens of published studies, and you don’t have time for that. 

You also might wonder if the data is being cherry-picked. Is this Carb Manager article just selecting Keto-friendly studies? Hmm.

To save time and skepticism, let’s look at one (and only one) 2020 paper published in the journal Nutrients. It’s called ”The Effect of Low-Fat and Low-Carbohydrate Diets on Weight Loss and Lipid Levels: A Systematic Review and Meta-Analysis,” It analyzes 38 studies relevant to the subject at hand.[*

The conclusion? Overall, low-carb diets are more effective for weight loss. They’re also more effective for lowering triglycerides and raising HDL cholesterol, both improvements in heart disease risk. Low-fat diets, to be fair, are more effective for lowering LDL and total cholesterol. 

Why might low-carb diets work for weight loss? A few things are going on. Low-carb diets:

  • Suppress hunger (people tend to eat less on Keto)[*]
  • Increase energy expenditure (you burn more calories at rest)[*]
  • Lower insulin levels (low insulin promotes fat burning)[*]
  • Tend to include more protein than low-fat diets (protein is highly satiating)

In combination, these factors make a promising recipe for weight loss. 

Low-Carb vs. Low-Fat Benefits

One potential benefit of a low-fat diet is a reduction in LDL cholesterol, a heart disease risk factor. Assuming you limit overall calories, reducing fat intake may also help with weight loss, but that’s true of any dietary program. 

The potential benefits of low-carb diets—and ketogenic diets specifically—include:

  • Fat loss (especially around the belly)[*]
  • Improved cognition[*]
  • More stable energy 
  • Reduced inflammation[*
  • Therapy for type 2 diabetes
  • Potential therapy for Alzheimer’s and cancer[*][*

But that doesn’t mean low-carb is for everyone. 

Potential Downsides of Low-Carb

Some people see a rise in LDL-cholesterol levels[*] on a low-carb diet, possibly denoting increased heart disease risk. Some people, however, see declines in LDL on Keto.[*

Also, because of the potential for calorie restriction and the suppression of insulin (a growth hormone), a low-carb or Keto diet isn’t ideal for: 

  • Pregnant and nursing women
  • Growing children 
  • Underweight people
  • Those with a history of eating disorders
  • Those looking to pack on muscle

People with issues digesting fat (liver issues, pancreas issues, gallbladder issues, etc.) may also want to lean towards higher carb intakes. 

One final downside of Keto is its restrictiveness. Some people struggle tremendously to give up carbs.

Potential Downsides of Low-Fat

Dietary fat is essential for structuring cell membranes, helping you absorb fat-soluble vitamins, and balancing the immune response. If you avoid fat too aggressively, these functions may suffer. 

For instance, the omega-3 fatty acids EPA and DHA both play important roles in promoting brain health and reducing inflammation.[*] The best sources of omega-3s are fatty fish like salmon and sardines.

Another problem with low-fat diets? They’re often high in refined carbohydrates. 

Unfortunately, high sugar diets have been linked to heart disease, type 2 diabetes, cancer, cognitive decline, liver disease, and most other chronic conditions.[*][*][*][*][*] Obesity too. Research indicates that the more sugar someone eats, the more likely they are to become obese.[*

This isn’t to claim that all carbs are bad for you. The people of Kitava Island (southwest of Papua New Guinea) are models of metabolic health on a diet of carb-rich yams, sweet potatoes, and taro.[*]

But refined carbs are different. These quickly-metabolized, highly-processed carbs don’t fill you up and keep you coming back for more - bad news for obesity and diabetes risk. 

Which Diet Should You Choose?

It depends. If you want to lose weight or experience the potential benefits of ketosis, low-carb diets are the better choice.

But if you can’t live without potatoes or have concerns about LDL cholesterol, you might try low-fat instead. 

Whichever diet you choose, focus on food quality. In many respects, the quality of your fats and carbs matters more than the quantity. 

In other words, eat whole foods until you’re full, and then stop until you’re hungry again. That’s the fundamental rule of healthy eating.