August 8, 2019

Why do low-carbohydrate diets work? An explanation of the underlying mechanisms

Warum funktionieren kohlenhydratarme Diäten? Eine Erklärung der zugrunde liegenden Mechanismen

Low carbohydrate diets work. This is currently a well-documented scientific fact. At least 23 high quality human studies have shown this. In many cases, a low-carb diet produces two to three times more weight loss than the standard low-fat diet that we are still universally told to follow (1, 2).

Low carbohydrate diets also appear to have an exceptionally good safety profile. There are no reports of serious side effects. In fact, studies even show that these diets bring significant improvements in many important risk factors (3). Triglyceride levels decrease and good HDL cholesterol levels increase. Blood pressure and blood glucose levels tend to decrease significantly (4, 5, 6, 7).

A higher percentage of the fat lost during a low-carb diet comes from the abdominal area and the liver. This is the dangerous visceral fat that accumulates around the organs and promotes inflammation and disease (8, 9, 10).

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

However, there is a lot of debate about why these diets work. People like to discuss the underlying mechanisms - the stuff that actually goes on in our organs and cells that ultimately leads to weight loss. Unfortunately, these mechanisms are not yet fully understood and there is a good chance that several things are working together. So it could very well be that there are many different reasons why these diets are so effective (11).

In this article, we will look at some of the most convincing explanations for the effectiveness of low-carb diets.

Carbohydrate restriction lowers insulin levels

Insulin is a very important hormone in the body whose main function is to regulate blood glucose levels and energy storage. One of the functions of insulin is to signal fat cells to produce and store fat, as well as to hold on to the fat that is already stored in them.

Insulin also signals other cells in the body to take up glucose (blood sugar) from the bloodstream and burn it instead of fat. Insulin therefore stimulates lipogenesis (the production of fat) and inhibits lipolysis (the burning of fat).

It is well documented that low-carbohydrate diets lead to a drastic and almost immediate reduction in insulin levels (12, 13). Here is a graph from a study on low-carbohydrate diets showing the course of insulin levels during a low-carbohydrate diet (red) and in a control group that followed a regular Western diet throughout the day (14).

According to many experts on low-carbohydrate diets including Gary Taubes and Dr. Atkins, lower insulin levels are the main reason for the effectiveness of low-carbohydrate diets. These experts claim that when carbohydrate intake is restricted and insulin levels drop, fat no longer remains "locked away" in fat cells and instead becomes available to the body as an energy source, resulting in a reduced need for food intake.

However, I would like to emphasize that many respected experts on obesity do not believe this to be true and therefore do not think that the carbohydrate-insulin hypothesis of obesity is supported by scientific data and studies.

Summary: Blood glucose levels and insulin levels drop significantly when carbohydrate intake is reduced. High insulin levels contribute to fat storage and low insulin levels promote fat burning.

Water weight drops rapidly at the start of a low-carb diet

During the first 1 to 2 weeks of a low-carb diet, dieters tend to lose weight very quickly. The main reason for this is a reduction in water weight.

The underlying mechanism involves two factors:

Insulin: When insulin levels drop, the kidneys begin to excrete excess sodium from the blood. This also lowers blood pressure (15).
Glycogen: The body stores carbohydrates in the form of glycogen, which binds water in the muscles and liver. When carbohydrate intake decreases, glycogen levels in the body also decrease and the water bound to glycogen is excreted.

This does not happen to nearly the same extent with a higher carbohydrate diet - even when calories are significantly reduced. Although some people use this as an argument against low-carb diets, reduced water weight should be seen as an advantage. Who wants to be overly bloated and carry around excess water weight all the time?

Despite claims to the contrary, this is far from being the main benefit of low carbohydrate diets in terms of weight loss. Studies clearly show that low-carbohydrate diets also lead to greater fat loss, especially the "dangerous" belly fat found in the abdomen. (8, 16).

Part of the weight loss benefits of low-carbohydrate diets can therefore be explained by a reduction in water weight, but there is also significant fat loss.

Summary: When people switch to a low-carbohydrate diet, they lose significant amounts of water stored in the body. This explains the rapid weight loss that can be observed during the first week or two.

Low carbohydrate diets are high in protein

In most studies comparing low-carbohydrate diets and low-fat diets, the low-carbohydrate group ended up consuming much more protein. This is because dieters replace many low-protein foods (grains, sugar) with higher-protein foods such as 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 (17, 18, 19, 20).

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

Summary: Low-carbohydrate diets tend to be much higher in protein than low-fat diets. Protein can reduce appetite, boost metabolism and help people maintain their existing muscle mass despite calorie restriction.

Low carbohydrate diets have a metabolic advantage

Although controversial, many experts believe that low carbohydrate diets have metabolic benefits. In other words, this means that low-carbohydrate diets would increase energy expenditure and that dieters should lose more weight than could be explained by the reduced calorie intake alone.

There are indeed some studies that support this. A 2012 study found that a very low-carbohydrate diet increased energy expenditure compared to a low-fat diet during a weight maintenance phase (21). This increase was around 250 kcal, which is roughly equivalent to the energy expenditure during one hour of moderate-intensity exercise.

However, another study suggested that it is the high protein intake (and not the low carbohydrate intake) of this type of diet that is responsible for the increase in energy expenditure (22).

However, there are other mechanisms that could result in a metabolic benefit. During a low-carbohydrate ketogenic diet, where carbohydrate intake is kept extremely low, a lot of protein is converted into glucose, at least initially, through a process called gluconeogenesis (23).

This is an inefficient process that can result in hundreds of calories being 'wasted'. However, this is only a temporary process, as within a few days of entering ketosis, the ketones produced begin to replace some of the glucose that the brain needs as an energy source (24).

Summary: Low-carbohydrate diets appear to have a metabolic advantage, but this is largely due to increased protein intake. Also, at the beginning of a low-carbohydrate ketogenic diet, some calories are wasted when glucose is made from protein.

Low-carb diets are less varied and provide less of a "reward response" to food intake

Low carbohydrate diets automatically exclude some of the worst "fattening" fast foods. This includes sugar, sugary drinks, fruit juices, pizza, white bread, chips, cakes and most unhealthy snacks.

There is also an obvious reduction in variety when most carbohydrate-rich foods are eliminated from the diet. It is well known that increased variety and diversity in food intake can increase calorie intake (25).

Many of these foods produce a strong 'reward response' and this can influence the amount of calories we ultimately consume (26). A reduced variety of food intake and a reduced intake of junk food with a high 'reward factor' should therefore reduce calorie intake.

Summary: Low-carbohydrate diets exclude many foods that have a high reward factor and are major fattening foods. These diets also have a lower variety of foods, which can lead to a reduced calorie intake.

Low carbohydrate diets significantly reduce appetite, which automatically leads to reduced calorie intake

Probably the most important explanation for the weight loss effect of low-carbohydrate diets is their significant effect on appetite. It is well documented that when people start a low-carbohydrate diet, their appetite decreases and they therefore automatically consume fewer calories (27).

Studies comparing low-carbohydrate and low-fat diets usually restrict calorie intake only in the low-fat group, while members of the low-carbohydrate group are allowed to eat until they are full (28). Despite this difference, the low-carbohydrate group usually loses more weight.

There are many possible explanations for this appetite-reducing effect, some of which we have already discussed. Increased protein intake is a primary factor, but there is also evidence that ketosis may have a powerful effect (29). Many people who follow a ketogenic diet feel that they only need 1 to 2 meals a day. They are simply not hungry more often.

There is also some evidence that low-carbohydrate diets have positive effects on appetite-regulating hormones such as leptin and ghrelin (30).

Summary: Low-carbohydrate diets can lead to an automatic reduction in calorie intake, so that dieters consume fewer calories without thinking about it.

The long-term effects on weight loss are not very impressive

Even though low-carb diets are very effective in the short term, the long-term results are not as good. Most studies lasting 1 to 2 years show that the difference between the low-carb groups and the low-fat groups disappears over time.

There are many possible explanations for this, but the most plausible is that people tend to give up the diet over time and start to regain the lost weight. This is not specific to low-carbohydrate diets and is a well-recognized problem in most long-term weight loss studies. Most diets are very difficult to maintain in the long term.

Conclusion

Most people refuse to accept that low-carb diets work and that people can eat as much as they want during these diets, as this seems to violate the "a calorie is a calorie" model.

However, when you understand the mechanisms underlying low-carb diets, you quickly realize that this model is not violated and the laws of thermodynamics continue to hold. The truth is that low-carb diets work on both sides of the calorie equation.

They stimulate metabolism (increasing calorie expenditure) and reduce appetite (reducing calorie intake), which automatically leads to calorie restriction. The calories still count - it's just that low-carb diets automate the process and help prevent the biggest side effect of deliberate calorie restriction - hunger.

References:

Source: https://www.healthline.com/nutrition/why-do-low-carb-diets-work#section8

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