Friday, January 1, 2010

Intermittent fasting and reduced inflammation

A recent post on the Primal Wisdom blog led me to do go back to some of the research on an approach to dieting that I tried myself, with some positive results. The approach is known as intermittent fasting (IF). I also found an excellent blog post by Dr. Michael Eades on IF (see here).

Typically IF involves fasting every other day. On the non-fasting days, food and water consumption is not restricted in any way. On fasting days, only water is consumed. Variations of this approach usually involve replacing water with juice, and having an eating window of only a few hours within longer periods – e.g., fasting 19 hours and then eating during a window of 5 hours, for each period of 24 hours.

IF is different from calorie restriction (CR), in that in the latter total daily calorie intake is restricted to a somewhat fixed amount, below one’s basal metabolic rate (the number of calories needed to maintain one’s current weight). In CR the calorie restriction is not normally achieved through fasting, but through careful portion size control and selection of foods based on calorie content. Having said that, some prominent CR practitioners also practice IF.

One interesting aspect of IF studies is that often they do not involve any calorie reduction in the participants' diet; that is, individuals consume the same amount of calories that they would if they were not fasting at all. In other words, they consume 2X outside their fasting window; where X would be their normal caloric consumption without fasting.

Yet, the benefits of IF are still achieved. For example, during Ramadan, the levels of inflammation markers and factors, such as C-reactive protein (CRP) and homocysteine, go down, and remain low for several weeks after IF is interrupted. These inflammation markers and factors are known to be strongly associated with heart disease.

In fact, animal studies suggest that virtually identical benefits can be obtained through IF in terms of increased lifespan and disease resistance, as those normally associated with CR. Again, this is somewhat surprising because often IF does not involve any reduction in calories consumed.

Fasting promotes increased levels of growth hormone in humans. A decline in growth hormone levels is associated with aging. Thus, increased circulating growth hormones may be one of the mechanisms by which IF may affect lifespan.

There have been some reports of IF being associated with negative effects on health, but I suspect that they are associated with gorging on refined carbohydrates and sugars during the eating window. Refined carbohydrates and sugars promote inflammation, and IF reduces inflammation. It is conceivable that a very high consumption of refined carbohydrates and sugars during the eating window may completely negate the benefits of IF, particularly if one is doing a half-hearted version of IF to start with.

A combination of IF and a diet low in refined carbohydrates and sugars probably makes sense in terms of our evolved physiology. Our Stone Age ancestors had to fast on a regular basis, based on the availability of food – there were no refrigerators or grocery stores during the vast majority of our evolutionary history as a species. When food was available, it was consumed to satiety. In other words, our Stone Age ancestors practiced IF, against their will. Because of that, this is the state in which our body evolved to operate optimally.

If you watch enough episodes of the TV show Survivorman, you will probably notice that it is very unlikely that our Stone Age ancestors had access to enough calories to survive on plant foods only, assuming that they faced problems similar to those in the show.

Our digestive tract has evolved over millions of years from a mostly vegetarian diet, practiced by our Australopithecine ancestors, to a primarily carnivorous diet, adopted by human ancestors as far back as Homo erectus, and probably Homo habilis. Given that, only the recent invention of refined carbohydrates and sugars has given us access to enough dense carbohydrate sources of calories.

So, a combination of IF and a diet low in (or devoid of) refined carbohydrates and sugars makes evolutionary sense, and is probably why so many people who adopt Paleolithic diets see so many improvements in health markers such as inflammation markers, blood pressure, and HDL cholesterol.


GH said...

"Fasting promotes increased levels of growth hormone in humans."

where did u hear this? i would have thought that fasting would lead to catabolism, not growth??

Ned Kock said...

The main driver of catabolism is lack of enough muscle exertion.

Fasting promotes the release of GH, and so does deep sleep. I discuss this in more detail the following posts:

GH said...

thanks. good blog this. not many readers judging by the lack of comments but probably cos it seems to be new. keep writing high quality articles and they will come...

Spencer said...

The two links to Dr. Eades' blog both point to the same post.

Ned Kock said...

Hi Spencer, thanks for pointing that out.

I revised the post to fix the repeated link problem.

Unfortunately I couldn't find the second post that I was referring to.

Anonymous said...

You said there have been some reports of negative health effects from IF. Could you elaborate and give cites? I'd like to see the details.

Ned Kock said...
This comment has been removed by the author.
Ned Kock said...

I don't have the refs now, but I am not even sure if the ones I've seen are relevant. If I recall them properly, they refer to half-hearted IF where there was also consumption of foods rich in refined grains, seeds, and sugars. In other words, those studies may not assess IF's health benefits, but whether IF can counter the damage done by highly processed foods.

Chris Kresser said...

I think IF is wise for most people. However, for those with low dysglycemia it may not be. In either hypoglycemia or reactive hypoglycemia, when the blood sugar drops (due to skipping a meal or several) the counter-regulatory hormones like cortisol, epinephrine, norepinephrine and glucagon kick in. If this happens repeatedly over time, it could contribute to inflammation and a host of other problems. That's why, in general, I think it's a good idea for people with these conditions to eat small, frequent meals throughout the day to keep their blood sugar stable and prevent the stress hormones from kicking in.

Ned Kock said...

Hi Chris.

There are divergent opinions on this, but the empirical evidence seems to generally point in the direction of no major problems related to IF in diabetics.

Since the post discusses Ramadan, this article is relevant:

Chris Kresser said...

I'm not referring to the effect of fasting on blood sugar, but rather the effect of chronic surges of stress hormones caused by that initial 10 point drop described in the article you linked to. For someone who is already hypoglycemic, a drop like that will certainly induce a sympathetic response, which over time stresses the adrenal glands. This kicks off a nasty vicious cycle. I've found in my clinical experience that hypoglycemics do better eating more frequently.

Also, in the paper you linked to the subjects continued taking oral medication for blood sugar control, and it was recommended that people who've experienced two episodes or more of hypoglycemia in the past during Ramadan not fast.

Ned Kock said...

Hi Chris.

But wouldn't that be a response associated with chronic fasting? I mean, IF may actually have a positive effect in some T2Ds if done occasionally.

I am reminded of this case of a child with a glycogen synthase (discussed in the post below), which was in constant and deep ketosis. Similar to a ketosis-prone T2D. The child apparently had no major health problems.

I don't doubt that your approach is much better than chronic fasting. There are quite a few people I know who swear by what they call "grazing", and say that they fell extremely miserable when they fast. Here in South Texas it seems that the majority of 40+ folks are either diabetic or on their way to becoming diabetic.

But sometimes what makes you feel good is not the best for you.

You are right, the article has a number of warnings at the end. They seem to think that obese T2Ds are the ones that could benefit the most.

Chris Kresser said...

It's an interesting question. In people with normal blood sugar control, chronic fasting would induce that sympathetic response. But I think it may happen even with IF in the case of hypoglycemics. I have not tracked this, though, with any kind of diagnostics other than my patients' symptoms.

My concern is that hypoglycemics almost always have some cortisol dysregulation as evidenced by a saliva test, and that IF *could* worsen this through repeated stress hormone surges.

For example, many of these patients can't sleep through the night. What seems to be happening is their blood sugar drops below normal in the early morning. Normally, cortisol would kick in to bring blood sugar back up. But if they aren't producing much cortisol (because their adrenals are shot), the body will secrete epinephrine instead to bring blood sugar to normal. This wakes them up. For these folks, eating something before bed (natural carbohydrate or protein) helps them sleep through the night.

Perhaps after struggling through an initial period of IF, it would actually help their blood sugar to normalize and ultimately reduce the adrenal stress they suffer from. I don't know.

kamagra said...

This is good because I didn't know this concept "intermittent" fasting, that's perfect that I can change water for other beverages when I'm doing an specif diet.m10m