Fasting and cholesterol


How can you lower cholesterol without medications? And what happens to your cholesterol if you do intermittent fasting?

High cholesterol is considered a treatable risk factor for cardiovascular disease such as heart attacks and strokes. There are many nuances to cholesterol which I do not want to get into, but traditionally, the main division has been 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, a type of fat found in the blood. Fat is stored in fat cells as triglycerides, but also floats around freely in the body. For example, during fasting, triglycerides get broken down into free fatty acids and glycerol. Those free fatty acids are used for energy by most of the body. So triglycerides are a form of stored energy. Cholesterol is not. This substance is used in cellular repair (in cell walls) and also used for to make certain hormones.

The Framingham Heart studies of the early 1960s established that high blood cholesterol levels as well as high triglycerides are associated with heart disease. This association is much weaker than most people imagine, but results were slightly improved when LDL was considered separately from HDL. Since cholesterol is found at the site of atheromatous plaques, the blockages in the heart, it seemed intuitive that high blood levels plays a role in ‘clogging up the arteries’.

The question, therefore, became, what causes high blood levels of cholesterol? The first thought was that high dietary intake of cholesterol would lead to high blood levels. This was disproven decades ago. One might (mistakenly) think that decreasing dietary cholesterol may reduce blood cholesterol levels. However, 80% of the cholesterol in our blood is generated by the liver, so reducing dietary cholesterol is quite unsuccessful. Studies going back to Ancel Key’s original Seven Country Studies show that how much cholesterol we eat has very little to do with how much cholesterol is in the blood. Whatever else he got wrong, he got this right – eating cholesterol does not raise blood cholesterol. Every single study done since the 1960s has shown this fact repeatedly. Eating more cholesterol does not raise blood levels.

However, it has taken far longer for this information to reach the public. Dietary Guidelines for Americans, published every 5 years, has repeatedly stressed lowering dietary cholesterol as if it made a difference. It doesn’t. So, if dietary cholesterol didn’t raise blood cholesterol, what did?

Low-fat diets and cholesterol

The next thought was that lowering dietary fat, especially saturated fats, may help lower cholesterol. While untrue, there are still many who believe it. In the 1960’s the Framingham Diet Study was set up to specifically look for a connection between dietary fat and cholesterol. This was 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 it, before? Well, the findings of this study showed no correlation between dietary fat and cholesterol whatsoever. Because these results clashed with the prevailing ‘wisdom’ of the time, they were suppressed and never published in a journal. Results were tabulated and put away in a dusty corner. Dr. Michael Eades was able to track down a copy of this forgotten gem and wrote about it’s eerily prescient findings here.

untitled-10But other studies throughout the next few decades found the same negative result. The Tecumseh study compared blood cholesterol levels to dietary fat and cholesterol. Whether blood levels were high, medium or low, each group pretty much ate the same amount of fat, animal fats, saturated fats and cholesterol. Dietary intake of fat and cholesterol does not influence blood cholesterol much.

In some studies, extremely low-fat diets can lower the LDL (bad cholesterol) slightly, but they also tend to lower the HDL (good cholesterol) so it is arguable whether overall health is improved. Other studies show no such lowering. For example, here’s a study in 1995, where 50 subjects were fed either a 22% or a 39% fat diet. Baseline cholesterol was 173 mg/dl. After 50 days of a low fat diet, it plummeted to… 173 mg/dl. Oh. High-fat diets don’t raise cholesterol much either. After 50 days of high fat diets, cholesterol increased marginally to 177 mg/dl.

Millions of people try a low-fat or low-cholesterol diet without realizing that these have already been proven to fail. I hear this all the time. Whenever somebody is told their cholesterol is high, they say “I don’t understand. I’ve cut out all fatty foods”. Well, reducing dietary fat will not change your cholesterol. We’ve known this for a long time. There are marginal changes at best. So, what to do? Statins, I guess?

“A little starvation can really do more for the average sick man than can the best medicines and the best doctors” – Mark Twain

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

Now, there are many controversies about lipids that I do not wish to get quagmired in. For example, there are many details about particle size and calculations of total particle numbers and newer particles etc. that are beyond the scope of this discussion. I will limit this discussion to the classic HDL/ LDL/ and triglycerides.


‘Good’ cholesterol (HDL) is protective, so the lower the HDL, the higher the risk of CV disease. This association is actually much more powerful than that for LDL, so let’s start here. bhutani2These are associations only, and HDL is simply a marker for disease. Drugs that raise HDL do not protect against heart disease, just as dying your hair does not make you younger.

Several years ago, Pfizer poured billions of dollars into researching a drug called torcetrapib (a CETP inhibitor). This drug had the ability to significantly increase HDL levels. If low HDL caused heart attacks, then this drug could save lives. Pfizer was so sure of itself, it spent billions of dollars trying to prove the drug effective.

The studies were done. And the results were breathtaking. Breathtakingly bad, that is. The drug increased death rate by 25%. Yes, it was killing people left and right like Ted Bundy. Several more drugs of the same class were tested and had the same killing effect. Just one more illustration of the ‘Correlation is not Causation’ truth.

Nevertheless, we care about HDL because it is a marker of disease, just as a fever is often the visible sign of an underlying infection. If HDL is decreased, then it may be a clue that the underlying situation is also worsening. What happens to HDL during fasting? You can see from the graph that 70 days of alternate daily fasting had a minimal impact upon HDL levels. There was some decrease in HDL but it was minimal.


The story of triglycerides (TG) is similar. TGs are markers of disease, but they do not cause it. Niacin is a drug that increases HDL and lower TG without very much effect on the LDL.

bhutani3The AIM HIGH study tested whether niacin would have any cardiovascular benefits. The results were stunning. Stunningly bad, that is. While they did not kill people, they did not help them either. And there were lots lot side effects. So, TG, like HDL is only a marker not a causer of disease.

What happens to TG during fasting? There’s a huge 30% decrease in TG levels (good) during alternate daily fasting. In fact, triglyceride levels are quite sensitive to diet. But it is not reducing dietary fat or cholesterol that helps. Instead, reducing carbohydrates seems to be the main factor that reduces TG levels.


The LDL story is much more contentious. The statin drugs lower LDL cholesterol quite powerfully, and also reduces CV disease in high risk patients. But these drugs have other effects, often called the pleiotropic (affecting multiple systems) effects. For example, statins also reduce inflammation, as shown by the reduction in hsCRP, an inflammatory marker. So, is it the cholesterol lowering or the pleiotropic effects that are responsible for the benefits?

This is a good question to which I do not have an answer yet. The way to tell would be to lower LDL using another drug and see if there are similar CV benefits. The drug ezetimibe in the IMPROVE-IT trial also had some CV benefits, but they were extremely weak. To be fair, the LDL lowering was also quite modest.

bhutani1A new class of drugs called the PCSK9 Inhibitors has the power to reduce LDL a lot. The question, though is whether there will be any CV benefit. Early indications are quite positive. But it is far from definitive. So the possibility exists that LDL may play a causal role here. This is, after all, why doctors worry so much about keeping LDL down.

What happens to LDL levels during fasting? Well, they go down. A lot. Over the 70 days of alternate daily fasting, there was about a 25% reduction in LDL (very good). To be sure, drugs can reduce them about 50% or more, but this simple dietary measure has almost half the power of one of the most powerful classes of medications in use today.

adf-musclemass1In combination with the reduction in body weight, preserved fat-free mass, and decreased waist circumference, it is clear that fasting produces some very powerful improvements in these cardiac risk factors. Don’t forget to add in the reduced LDL, reduced triglycerides and preserved HDL.

But why does fasting work where regular diets fail? Simply put, during fasting, the body switches from burning sugar to burning fat for energy. Free fatty acids (FFA) are oxidized for energy and FFA synthesis is reduced (body is burning fat and not making it). The decrease in triacylglycerol synthesis results in a decrease in VLDL (Very Low Density Lipoprotein) secretion from the liver which results in lowered LDL.

The way to lower LDL is to make your body burn it off. The mistake of the low-fat diet is this – feeding your body sugar instead of fat does not make the body burn fat – it only makes it burn sugar. The mistake of the Low-Carb, High-Fat diet is this – giving your body lots of fat makes it burn fat, but it will burn what’s coming into the system (dietary fat). It won’t pull the fat out of the body.

Here’s the bottom line for those big-picture, spare-me-the-details kind of folks. Fasting has the following effects:

  1. Reduces weight
  2. Maintains lean mass
  3. Decreases waist size
  4. Minimal change in HDL
  5. Dramatic reductions in TG
  6. Dramatic reductions in LDL

That’s all good. Whether this will all translate into improved cardiac outcomes, I don’t have the answer for you. My guess is Yes.

However, fasting always boils down to this. There are all these benefits. There’s very little risk. What do you have to lose (other than a few pounds)?

For people worried about heart attacks and strokes, the question is not “Why are you fasting?”, but “Why are you NOT fasting?”

Jason Fung


Intermittent fasting for beginners

Popular videos about fasting

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Earlier with Dr. Jason Fung

The calorie debacle

Fasting and growth hormone

The Complete Guide to Fasting is finally available!

How does fasting affect your brain?

How to renew your body: Fasting and autophagy

Complications of diabetes – a disease affecting all organs

How much protein should you eat?

Practical tips for fasting

The common currency in our bodies is not calories – guess what it is?

More with Dr. Fung

Dr. Fung has his own blog at He is also active on Twitter.

His book The Obesity Code is available on Amazon.

The Obesity Code

His new book, The Complete Guide to Fasting is also available on Amazon.



  1. Serge Fernandes
    Hi Dr. Jason Fung,

    Thanks for your publication.

    Im 32 years old and I have been Fasting for about 1 year. I eat only vegetable which grows above the ground, eat dairy products (real ones), cook with coconut oil or butter and the only high glycemic food I eat is on the breakfast (1 small banana). I love avocado, nuts and seeds...not all seeds.

    I read your publication and I am said because for me it didn't work well...Is not a matter about weight loss because I am a big sportive with around 11 hours of training per week. I do endurance sports it is why I am very interested in Fasting diet...

    In my last results of blood sample my total cholesterol rise a lot...almost the double if I compare with the last year blood sample exams and my LDL is quite high too...above the limits for people with my age. That's true that my HDL raised a lot and my Tryglicerides decreased too.

    What is for you the normal values of HDL, LDL, TOTAL and tryglicerides in a blood sample? Or the ratio between them?

    Thanks a lot


    Reply: #4
  2. gbl
    Therapeutics Initiative is a non-industry funded site from the University of British Columbia medical school which assesses benefits and harms of all the most prescribed drugs. Clinical pharmacologist and Cochrane Collaboration hypertension head Dr. James Wright leads Therapeutics Initiative. This is gold-standard information that our doctors can't dismiss:

    Steve thank you for this very well-researched report. Best of luck.

  3. gbl
    PPS: Thanks too for your links on global warming which I am presenting studying. I thought I'd add science to the devastation that I have observed with my own eyes.
  4. Peter Biörck Team Diet Doctor
    Hi Serge!

    If you are a member you can direct a question to Dr Fung here:

    Hi Dr. Jason Fung,
    Thanks for your publication.
    Im 32 years old and I have been Fasting for about 1 year. I eat only vegetable which grows above the ground, eat dairy products (real ones), cook with coconut oil or butter and the only high glycemic food I eat is on the breakfast (1 small banana). I love avocado, nuts and seeds...not all seeds.
    I read your publication and I am said because for me it didn't work well...Is not a matter about weight loss because I am a big sportive with around 11 hours of training per week. I do endurance sports it is why I am very interested in Fasting diet...
    In my last results of blood sample my total cholesterol rise a lot...almost the double if I compare with the last year blood sample exams and my LDL is quite high too...above the limits for people with my age. That's true that my HDL raised a lot and my Tryglicerides decreased too.
    What is for you the normal values of HDL, LDL, TOTAL and tryglicerides in a blood sample? Or the ratio between them?
    Thanks a lot

  5. Chad
    The niacin study link referenced fails to mention what form of niacin was used. I’m assuming they were using the non flush variety nicotinamide or it would be quite difficult to have a placebo group with only half of the people turning red. Both forms of niacin will help severe niacin deficiency (Pellagra) however they are not identical. ive heard that the flush form, nicotinic acid is beneficial for cv and and the other is not.
  6. Angie Johnson
    Hello. I have done the 24 hour fast one day a week for the last 6 weeks. I also did one 36 hour fast. In my research, I am finding conflicting messages with regard to LDL. Here is an article where the person experimenting with their own body LDL increased drastically. I am not trying to mess up my health nit knowing if this is the right thing to do or not. Frustrating. PLEASE HELP!

  7. Szymonkb
    Hey Angie. If you fast 1 day in 7 days how do you expect it to make any effect? 6/7 of week of junkfood diet with one day off won't also give any health benefits. Try intermittent fasting which gives daily benefits - eating 3 meals only no eating between letting your body fast, detoxify, rebuild, recycle over 16 hours daily - burning fat many hours for real. The real change requires resolve and the actual change of previous habits. It is not a magic pill that fixes everything instantly and let you go to what made you sick or overweight back. It takes time, changes, rethinking old lifestyle and a decission to change life for better without distractions and old programs taking over again, reading and taking care of yourself yourself. If it works it works. Bad is bad, good is good, if it works it works if not it's not. But first step is to try for real.
  8. Hati
    I have been fasting continuously for 50 days before the test. Typically 16 hours fast from the last meal to first meal the next day. I’m slightly underweight (BMI - 18). But my cholesterol level increased from 213 to 230.
  9. Maika
    7 Day Water Fast resulting in Elevated Cholesterol/LDL/Triglycerides

    I just ran an experiment where I only consumed Water/Coffee/Daily Multivitamin/Electrolyte Supplement (Noncaloric, Na, K, Mag, Ca, etc) for 7 Days.

    My Labs on the 7th day
    Cholesterol 147 -> 228
    HDL 46 -> 40
    LDL Calculated 90 -> 162
    Triglycerides 53 -> 128

    Average Daily
    Glucose Readings 60-80
    Ketones 1.5 - 2.5

    I've been practicing intermittent fasting (16:8) and omad (one meal a day) for 75% of the last 8 months or so, implementing a High Fat, Low Carb diet most of the time as well, prior to the fast.

    My interpretation of my results
    Elevated Cholesterol: With Cholesterol being such an agent of healing and hormone creation, I think my body had upper range of it due to possible increased steroid hormone production and possible increased cell membrane repair.

    Decreased HDL: HDL to my understanding takes cholesterol from the blood stream to the liver to be processed to make bile. If I'm not ingesting anything, then I'd expect this value to decrease because of the decrease in need to make bile.

    Increased LDL: I've been learning of the many variations of LDL, and how they are water soluble making them essential to transport triglycerides and cholesterol. So I'd expect on increase in this due to fat being the main source of fuel circulating in my blood stream.

    Increased Triglycerides: Ketone production to my understanding needs free fatty acids to be converted into ketones. I assume that an elevated level of triglycerides is due to the demand to make ketones (barring the triglycerides are readily broken down to a glycerol and 3 free fatty acids for ketogenesis and gluconeogenesis).

    I've listened to many different theories of normal lab values shifting to a new normal when on a Ketogenic Diet. For when you use fat as energy and increase cholesterol and saturated fat intake, while restricting carbohydrates, your body can respond differently but still in a healthy way.

    I was wondering if anyone has come across anything like this and have their own explanation? Thank you!


    Replies: #12, #15
  10. Amos Oliver Doyle
    Fasting does not always lower LDL, in fact it more likely will raise it, although there may be a certain population of people who are more likely to have increased LDL than others. All parts of the puzzle are not known yet. It is a mistake to think we have a definitive answer to heart disease, fats and cholesterol.
  11. Jacqueline Patti
    I suspect you may not have read the entire niaspan study.

    My cardiologist kept saying no to niaspan because this study showed it didn't reduce events. After a few years, I got curious and went and looked up the study, and it turns out that both the control and experimental group were on statins. So niaspan doesn't reduce events *over* a statin, but it's likely you could've done the reverse experiment and proved statins didn't reduce events over niaspan.

    Course the NNT isn't great for statins anyway.

    My triglycerides have improved after 3 months of fasting and ridiculously big salads (RBSs), but are still bad. I'm vaguely considering going back on niaspan; my hesitation is just that the pills are so damned big, it's irritating.

    But I fully expect them to drop further as I continue the fasting and RBSs. After my initial 11-day fast, I eventually settled into 3 days fasting/4 days OMAD, usually the RBS, each week. I expect I'll keep improving, though I'm admittedly impatient.

  12. Alberto
    Hey Maika, I got pretty much the same results and I was thinking about the same a an explanation. I was wondering how did it go for you during this time. Would love to chat about it.
  13. sylviamvdb
    Maika and Alberto, the same for me.
    I'm on intermittent fasting for 2 months 18-6 every day with drinking so much more water than I normally do. Bloodtest: LDL went up from 167 to 189 and triglycerides from 58 to 106!!!
    Is it because burnt fat is now in the blood or is this really worrying?
  14. Nuno
    I am doing 16:8 regularly and see the cholesterol raise too.
    Any new ideas?
    Reply: #16
  15. Nuno

    I'm in the same situation and was wondering what evolution you had.
    If you can post some more info I'd appreciate

  16. Kerry Merritt Team Diet Doctor

    I am doing 16:8 regularly and see the cholesterol raise too.
    Any new ideas?

    Our cholesterol guide may be helpful for you!

  17. Milan
    What do you think about this study?
    Thanks, Milan

    Reply: #18
  18. Dr. Bret Scher, MD Team Diet Doctor
    HI Milan. Thanks for your question. It is interesting that short term fasting can cause a rise in LDL cholesterol. That actually fits well with Dave Feldman's energy hypothesis, i.e when we are using fat for fuel, we need more fat delivery particles like VLDLs which eventually become LDL particles. However, when it comes to health risks and benefits, short term changes in LDL are likely less impactful than longer term changes. So, I am not clear on what long term effect this has. But it is certainly fascinating from a physiology standpoint!
    Bret Scher MD FACC Medical Director
    Reply: #19
  19. Milan
    Thank you very much Dr.Bret !
    Yes, Its a good point. Maybe it just a survive mechanism for the body, and the cholesterol work as a part of energy system.

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