As a dietitian, I often see patients who fast, but whose cholesterol levels are not improving despite their efforts. This article reviews some of the other mechanisms that can affect cholesterol levels, and illustrates how fasting can influence these mechanisms.

Fasting, which is the deliberate restriction of all or a portion of the caloric intake, is a common practice among health-conscious people. Some religious groups, such as the Seventh Day Adventists, practice periodic fasting. Some groups of people use fasting as a means of personal spiritual development. Fasting is also used as a form of punishment for various crimes, and as a means of punishing gladiators or prisoners of war.

How can I lower my cholesterol without taking medication? And what happens to your cholesterol levels when you do intermittent fasting?

High cholesterol is considered a treatable risk factor for cardiovascular disease, such as heart attack and stroke. Cholesterol has many nuances that I won’t go into, but traditionally the main classification is between low-density lipoprotein (LDL), or bad cholesterol, and high-density lipoprotein (HDL), or good cholesterol. Total cholesterol gives us little useful information.

We also measure triglycerides, the type of fat that is in the blood. Fats are stored in fat cells as triglycerides, but they also float freely in the body. For example, fasting breaks down triglycerides into free fatty acids and glycerol. These free fatty acids are used by a large part of the body as a source of energy. Triglycerides are thus a form of stored energy. Cholesterol, no. This substance is used for cell repair (in cell walls) and for the production of certain hormones.

The Framingham study, conducted in the early 1960s, found that high blood cholesterol and triglyceride levels were linked to heart disease. This link is much weaker than many think, but the results are slightly better when LDL is considered separately from HDL. Since cholesterol is found at the site of atherosclerotic plaques – blockages in the heart – it seemed intuitive that high levels of cholesterol in the blood play a role in clogging the arteries.

So the question arises: What causes high cholesterol? It was originally thought that a high dietary intake of cholesterol would lead to high blood cholesterol levels. This was debunked decades ago. You may think (wrongly) that by lowering the cholesterol in your diet, you can lower your blood cholesterol levels. However, 80% of the cholesterol in our blood is produced by the liver. Therefore, it is rather unfortunate to reduce cholesterol in the diet. Studies dating back to Ansel Kee’s first seven-country study show that the amount of cholesterol in the diet is barely related to the amount of cholesterol in the blood. Whatever he did, he did correctly: consuming cholesterol does not raise blood cholesterol levels. All studies conducted since the 1960s have proven this fact time and time again. Eating more cholesterol does not raise blood cholesterol levels.

However, it took much longer for this information to reach the public. The Dietary Guidelines for Americans, published every 5 years, repeatedly emphasize lowering dietary cholesterol as if it were the most important thing. That’s not the case. So if dietary cholesterol doesn’t raise blood cholesterol, what does?

Low-fat and low-cholesterol diets

The next idea was that reducing fat in the diet, especially saturated fat, could help lower cholesterol. Although this is not true, many people still believe it. In the 1960s, the Framingham Diet Study was conducted to investigate a link between dietary fat and cholesterol. This is the same Framingham as the famous heart studies, but references to the Framingham diet study are virtually non-existent. Why haven’t you heard of this before? The results of this study showed no correlation between dietary fat and cholesterol. Because these results were contrary to the prevailing wisdom of the time, they were suppressed and never published in professional journals. The results were added up and stored away in a dusty corner. Dr. Michael Eads managed to find a copy of this forgotten gem and has written about his amazingly prescient findings here.

But other studies in subsequent decades showed the same negative result. The Tecumseh study compared blood cholesterol levels with dietary fat and cholesterol levels. Whether blood levels were high, medium or low, each group consumed nearly the same amount of fat, animal fat, saturated fat and cholesterol. Dietary intake of fat and cholesterol has no significant effect on blood cholesterol levels.

In some studies, extremely low-fat diets can lower LDL cholesterol (bad cholesterol) somewhat, but they also tend to lower HDL cholesterol (good cholesterol), so the issue of improving overall health is moot. Other studies do not indicate such a decline. For example, there is a 1995 study in which 50 subjects were fed a diet containing 22% or 39% fat. The cholesterol level at baseline was 173 mg/dL. After 50 days on a low-fat diet, it dropped to ….. 173 mg/dl. О. Moreover, high-fat diets do not increase cholesterol levels. After 50 days on a high-fat diet, cholesterol levels rose slightly to 177 mg/dL.

Millions of people try low-calorie or low-cholesterol diets without knowing that they have already been proven to fail. I hear that all the time. When you tell someone they have high cholesterol, they react: I don’t understand. I stopped eating all the fatty foods. Reducing the amount of fat in your diet will not change your cholesterol levels. We’ve known that for a long time. At best, the changes are insignificant. What needs to be done? Probably statins?

A little fasting can really do more for the average patient than the best drugs and the best doctors – Mark Twain

Studies show that fasting is a simple dietary strategy that can significantly lower cholesterol levels.

There is a lot of discussion about lipids that I don’t want to get into. There are z. B. many details of particle size and calculations of total number of particles, newer particles, etc. which are beyond the scope of this discussion. I will limit this discussion to the classic HDL/ LDL/ and triglyceride levels.


Good cholesterol (HDL) is protective, so the lower the HDL level, the higher the risk of CV disease. This link is actually much stronger than the LDL link, so let’s start there. These are just associations, and HDL is just a marker of disease. Medications that increase HDL levels don’t protect against cardiovascular disease, just like dyeing your hair doesn’t make you look younger.

Several years ago, Pfizer invested billions of dollars in research for a drug called torcetrapib (a CETP inhibitor). This drug had the ability to significantly increase HDL levels. When low HDL levels lead to heart attacks, this drug can be life-saving. Pfizer was so convinced that it spent billions of dollars to prove the drug’s effectiveness.

Studies have been conducted. And the results are spectacular. It’s spectacularly bad. The drug increased the mortality rate by 25%. Yeah, he was killing people left and right, like Ted Bundy. Several other drugs of the same class have been tested and have had the same lethal effect. Another illustration of the truth: correlation is not causation.

However, we are interested in HDL because it is a marker of disease, just as fever is often a visible sign of an underlying infection. If HDL is low, it may be a sign that the underlying condition is also getting worse. What happens to HDL during fasting? The graph shows that 70 days of alternate daily fasting had a minimal effect on HDL levels. A slight decrease in HDL levels was observed, but it was minimal.


The history of triglycerides (TG) is similar. TGs are markers of disease, but do not cause it. Niacin is a drug that increases HDL and decreases TG, but has little effect on LDL.

The AIM HIGH study tested whether niacin had cardiovascular benefits. The results were overwhelming. Unbelievably bad. They didn’t kill people, but they didn’t help them either. And there were a lot of side effects. So TG, like HDL, is only a marker and not a cause of disease.

What happens to TG during fasting ? With daily alternate fasting, there is a huge 30% reduction in Tg levels (good). In fact, triglyceride levels are quite sensitive to diet. But it’s not reducing fat or cholesterol that helps. On the contrary, carbohydrate restriction seems to be the most important factor in lowering TG levels.


The history of LDL is much more controversial. Statins are very effective in lowering LDL cholesterol levels and also reduce the incidence of cardiovascular disease in high-risk patients. But these drugs have other effects, often called pleiotropic agents (they act on different systems). Statins also reduce inflammation, for example, as evidenced by reduced levels of hsCRP, a marker of inflammation. So what is the cause of this benefit – cholesterol reduction or pleiotropic effects?

That’s a good question and I don’t have an answer yet. To determine this, lower LDL levels with another drug and see if WS has a similar benefit. The drug ezetimibe in the IMPROVE-IT trial also showed some benefit for WS, but it was extremely small. To be fair, the reduction in LDL levels was also very modest.

A new class of drugs called PCSK9 inhibitors can significantly lower LDL levels. However, the question is whether the summary will be useful. The first signs are very positive. But this is far from definitive. So it is possible that LDL plays a causal role here. After all, that’s why doctors are so concerned about lowering LDL levels.

What happens to LDL levels during fasting? Well, they’re coming down. Very much so. Over 70 days of alternating daily fasting resulted in a reduction in LDL levels of about 25% (very good). Of course, drugs can reduce it by 50% or more, but this simple dietary measure has almost half the power of one of the most powerful classes of drugs in use today.

When combined with reduced body weight, maintenance of lean body mass, and reduced waist circumference, it is clear that fasting results in a very strong improvement in these cardiac risk factors. Don’t forget to add LDL lowering, triglyceride lowering and HDL maintenance.

But why does starvation work where conventional diets fail? Simply put, during fasting, the body switches from burning sugar to burning fat for energy. Free fatty acids (FFAs) are oxidized to produce energy, and the synthesis of FFAs is reduced (the body burns fat instead of producing it). Decreased triacylglycerol synthesis leads to decreased secretion of very low density lipoproteins (VLDL) by the liver, resulting in lower LDL levels.

The way to lower LDL levels is to get your body to burn it. The flaw in the low-fat diet is this: By feeding your body sugar instead of fat, it doesn’t burn fat, only sugar. The mistake with low-carb, high-fat diets is this: If you give your body lots of fat, it will burn fat, but it will burn what gets into your system (dietary fat). It does not extract fat from the body.

Here are the essentials for those who see things in large print and do not pay attention to the details. Fasting has the following effects:

  1. Reduces weight
  2. Preservation of lean body mass
  3. Reduces the size
  4. Minimal change in HDL levels
  5. Significant reduction in TG
  6. Significant reduction of LDL levels

It’s all right, it’s all right. I cannot tell you if this leads to better heart results. I think it is.

But fasting always comes down to this. All these advantages are present. The risk is very low. What do you need to lose weight (other than a few pounds)?

For those concerned about heart attacks and strokes, the question is not an issue: Why are you fasting but: Why don’t you go fast?

Jason Fung

Frequently Asked Questions

How does fasting affect cholesterol?

Fasting can help lower cholesterol levels.

Does intermittent fasting help lower cholesterol?

Some studies have shown that intermittent fasting can help lower cholesterol levels.

Does intermittent fasting increase cholesterol levels?

Some studies have shown that intermittent fasting can increase cholesterol levels. However, other studies have shown that intermittent fasting does not increase cholesterol levels.

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