Why Do Low Carb Diets Work? the Mechanism Explained

By Kris Gunnars, authoritynutrition.com
April 14, 2015 Updated: April 14, 2015

Low-carb diets work.

That is pretty much a scientific fact at this point.

At least 23 high quality studies in humans have shown this to be true.

In many cases, a low-carb diet causes 2-3 times more weight loss as the standard low-fat diet that we’re still being told to follow.

Low-carb diets also appear to have an outstanding safety profile. No serious side effects have been reported.

In fact, the studies show that these diets cause major improvements in many important risk factors.

Triglycerides go way down and HDL goes way up. Blood pressure and blood sugar levels also tend to decrease significantly.

A high percentage of the fat lost on a low carb diet comes from the belly area and the liver. This is the dangerous visceral fat that builds up in and around the organs, driving inflammation and disease.

These diets are particularly effective for people with metabolic syndrome and/or type 2 diabetes. The evidence is overwhelming.

However, there is a lot of controversy about why these diets work.

People like to debate the mechanism, the stuff that is actually going on in our organs and cells that makes the weight go off.

Unfortunately, this is not fully known, and chances are that it is multifactorial – as in, there are many different reasons why these diets are so effective.

In this article, I take look at some of the most convincing explanations for the effectiveness of low carb diets.

Carb Restriction Lowers Insulin Levels

Insulin is a very important hormone in the body.

It is the main hormone that regulates blood sugar levels and energy storage.

One of the functions of insulin is to tell fat cells to produce and store fat, and to hold on to the fat that they already carry.

It also tells other cells in the body to pick up glucose (blood sugar) from the bloodstream, and burn that instead of fat.

So, insulin stimulates lipogenesis (production of fat) and inhibits lipolysis (the burning of fat).

It is actually well established that low-carb diets lead to drastic and almost immediate reductions in insulin levels.

Here is a graph from one study on low-carb diets.

boden-insulin-levels
(Diet Doctor)

According to many experts on low-carb diets, including Gary Taubes and the late Dr. Atkins, lower insulin levels are the main reason for the effectiveness of low-carb diets.

They have claimed that, when carbs are restricted and insulin levels go down, the fat isn’t “locked” away in the fat cells anymore and becomes accessible for the body to use as energy, leading to reduced need for eating.

However, I’d like to point out that many respected obesity researchers do not believe this to be true, and do not think the carbohydrate-insulin hypothesis of obesity is supported by the evidence.

Bottom Line: Blood levels of the hormone insulin go way down when carb intake is reduced. High insulin levels contribute to fat storage, and low insulin levels facilitate fat burning.

(Shutterstock)
Part of the weight loss advantage of low-carb diets is explained by reductions in water weight. (Shutterstock)

 

Water Weight Drops Rapidly in The Beginning 

In the first 1-2 weeks of low carb eating, people tend to lose weight very quickly.

The main reason for this is reduction in water weight.

The mechanism behind it is two-fold:

  1. Insulin: When insulin goes down, the kidneys start shedding excess sodium from the body. This also lowers blood pressure.
  2. Glycogen: The body stores carbs in the form of glycogen, which binds water in the muscles and liver. When carb intake goes down, glycogen levels in the body go down, and the water follows along.

This does not happen to nearly the same extent on a higher carb diet, even if calories are reduced significantly.

Even though some people use this as an argument against low-carb diets, reduced water weight should be considered an advantage.

I mean, who wants to carry around excess bloat and water weight all the time?

Anyway, despite claims to the contrary, this is far from being the main weight loss advantage of low-carb diets.

The studies clearly show that low-carb diets lead to more fat being lost as well, especially the “dangerous” belly fat found in the abdominal cavity.

So, part of the weight loss advantage of low-carb diets is explained by reductions in water weight, but there is still a major fat loss advantage as well.

Bottom Line: When people go low-carb, they lose significant amounts of excess water from their bodies. This explains the rapid weight loss seen in the first week or two.

(Shutterstock)
Many nutrition experts believe that the high protein content of low-carb diets is the main reason for their effectiveness. (Shutterstock)

 

Low Carb Diets Are High in Protein 

In most studies where low carb and low fat diets are compared, the low carb groups end up eating much more protein.

This is because people replace many low-protein foods (grains, sugars) with higher protein foods like meat, fish and eggs.

Numerous studies show that protein can reduce appetite, boost metabolism, and help increase muscle mass, which is metabolically active and burns calories around the clock.

Many nutrition experts believe that the high protein content of low-carb diets is the main reason for their effectiveness.

Bottom Line: Low carb diets tend to be much higher in protein than low fat diets. Protein can reduce appetite, boost metabolism and help people hold on to muscle mass despite restricting calories.

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