Intermittent Fasting Shown To Improve Insulin Sensitivity!

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The impact an Intermittent Fasting (IF) eating plan can have on health parameters and performance levels has only been inestigated in a limited number of human trials to date. Whilst much more work needs to be done, early results seem to show that IF can significantly improve your insulin sensitivity.

Insulin resistance is a widespread problem in the developed world and it is now well established that insulin resistance is a preceding stage to type 2 diabetes.

A number of factors are implicated in people developing insulin resistance – diets containing hydrogenated and refined vegetable fats, too much fructose and sugar, and low levels of minerals involved in insulin action like chromium and magnesium have been shown to lower insulin sensitivity. In my opinion, a very obvious factor is the widespread vitamin d deficiency epidemic that we have nowadays.

Some theorise that another reason for the insulin resistance problem we face is simply an overabundance of food available to people. The theory goes that, because are genome was likely selected in the Paleolithic era (50,000–10,000 BC), where we had to hunt for food, our metabolisms are designed to work best on a feast-famine cycle where we have to go for longish periods without eating.

A group of Danish researchers set out to test whether following a hunter gatherer diet pattern that provided enforced breaks from eating could improve subjects’ insulin sensitivity (1):

Eight young men fasted every second day for 20 h, from 10 pm to 6pm the next day, for 15 days. Euglycemic hyperinsulinemic clamps were performed before and after the intervention period to measure insulin sensitivity (this is the best method in existence for testing insulin sensitivity). The results were as follows:

• 'After the 20-h fasting periods, plasma adiponectin was increased compared with the basal levels before and after the intervention (5,922 ± 991 vs. 3,860 ± 784 ng/ml, P = 0.02).'

• 'Insulin-mediated whole body glucose uptake rates increased from 6.3 ± 0.6 to 7.3 ± 0.3 mg•kg–1•min–1 (P = 0.03), and insulin-induced inhibition of adipose tissue lipolysis was more prominent after than before the intervention (P = 0.05).'

These results show that Intermittent Fasting can bring about impressive increases in both the action of insulin and in insulin sensitivity.

Adiponectin is believed to be a key marker of insulin sensitivity in humans - as levels of plasma Adiponectin increase whole body insulin sensitivity also increases.

Researchers have found that, unlike leptin, its tissue expression and and its plasma concentration are decreased (not increased) in obesity and diabetes.(2)

It appears that by incorporating fasting periods into your daily routine plasma adiponectin levels go up and both insulin action and sensitivity improve correspondingly.

Side note: Regular coffee and/or tea drinking has also been shown to raise plasma adiponectin levels and to improve your insulin sensitivity.

Whilst there needs to be more research done before we can determine the exact relationship between adiponectin and the performance of the hormone insulin in humans, scientists suggest that ‘the replenishment of adiponectin might provide a novel treatment modality for insulin resistance and type 2 diabetes.’ (3)

Other scientists have found that ‘in isolated hepatocytes, Acrp30 (adiponectin) increases the ability of sub-physiological levels of insulin to suppress glucose production.’(4) – this may mean that people with a damaged pancreas or blood sugar regulatory system might be able to manage their symptoms though Intermittent Fasting. I have actually read a few client testimonials on the Lean Gains website from diabetics who have found Martin Berkhan’s Intermittent Fasting diet structure helpful to them.

This study is applicable to body builders and athletes

One thing I like about this study is that it was performed on healthy young men between the ages of 24 to 26 years old – it’s trials like this, rather than trials done on older people, that might convince athletes and bodybuilders that Intermittent Fasting could be a way for them to improve upon their current physique and performance bests.

By the way, this does not mean that I think Intermittent Fasting will only work for you if your 25! Given that most of the research done on IF is primarily interested in whether it can extend life in the way calorie restriction is hypothesised to do, older people should certainly keep an eye on future research, or just give IF a try and see how they feel.

Improved insulin action

The fact that ‘insulin-induced inhibition of adipose tissue lipolysis was more prominent after than before the intervention’ is not necessarily, as you might initially assume, a bad thing. This shows that insulin action is improved and it is storing glucose and amino acids more effectively than before.

It is important to remember that insulin is a storage hormone and it is highly anabolic in both the muscle and fat departments. You will build more muscle and store more fat when you eat following a fast period, but you will burn more muscle and fat when fasting – it will probably level out.

From a health perspective, the better insulin is at disposing of glucose, either into the muscle or fat cells, the better. Elevated blood sugar levels are bad news and you want insulin working at peak condition to stop this from happening.

From a fat loss perspective, an insulin spike created by a meal is one signal given by your body that you have eaten enough calories – a more powerful insulin spike may signal you to eat less calories and this would help you to lose weight.

But no body fat lost?

Whilst these results definitely indicate that Intermittent Fasting improves insulin action and sensitivity, somewhat surprisingly the participants’ body weights and body fat percentages remained the same. Given that most of you are going to want to see a loss of body fat if you take up an IF eating plan these results might be slightly off putting.

All I can say about this is that the trial was only 15 days long– possibly the body composition benefits of Intermittent Fasting might be seen after a slightly longer period. Also bear in mind that other trials have found that IF eating regimes result in fat loss in humans even when calorie levels are kept constant(5).

Even if the only reason people are losing fat easily when doing IF is because they are maintaining a calorie deficit I don’t think this undermines IF at all – any eating pattern that makes maintaining a calorie deficit easier should be highly valued by dieters.

Intermittent Fasting in the real world...

In practise, what many are finding is that by adopting IF eating schedules (two examples being ‘Lean Gains’ and ‘The Warrior Diet’) they can suddenly lose fat much more quickly than previously without losing much, if any, muscle.

People who take up IF often talk about experiencing a simultaneous tightening of the waist and widening of the shoulders, and it is suggested by trainers experienced with IF that this is due to a better partitioning of nutrients towards muscle building and away from fat gain. Some suggest this is caused by IF improving your insulin sensitivity, others say it is because protein is used more effectively after fasting – maybe it is a combination of the two…

Ori Hofmekler, author of the ‘Warrior Diet’ and ‘Maximum Muscle, Minimum Fat’, talks about a process he terms as ‘protein shifting’. He argues that when fasting the body can actually redesign itself in order to maintain maximum performance by shifting protein from less active muscles to active muscles. He suggests that if you work out and incorporate IF the muscles your working will receive protein from your inactive muscles.

I don’t have much to back this theory up but if it’s true it would certainly explain how people doing IF claim to be becoming more muscular without gaining fat.

Can’t you get the same results just by exercising?

Some writers are suggesting that all of the benefits of Intermittent Fasting can be achieved much more easily simply by exercising, and this was actually something these Danish researchers looked at. They made the following conclusions:

‘The mechanism by which physical training increases whole body insulin sensitivity is not known in detail. It has previously been shown that in muscle the effect is mediated via local contraction dependent mechanisms (11–13), and this could include exercise-induced oscillations in local energy stores.

However, the insulin-sensitizing effects of exercise and intermittent fasting may not exert their effects via the same pathway. Although the local effect of exercise is well proven (there is no transfer of training-induced increase in insulin sensitivity to nontrained muscle), it is less likely that the effect of intermittent fasting is a local, muscle phenomenon. Thus even though we were not able to detect changes in muscle glycogen and triglyceride content after 20-h fasting, the intervention may still have exerted the effects via oscillations in other energy stores (e.g., in adipose tissue or liver).’

This is actually not that surprising since it has been shown that exercise does not alter plasma adiponectin levels(6). It seems for you to have the best of all worlds, improved whole body and improved muscle insulin sensitivity, you should both practise IF and workout out with weights – I can attest that this combination works.

Final Note

This study is one of a few recent studies that shows IF can significantly improve your insulin sensitivity, and this is something we all should be aiming at for both our body compositions and overall levels of health.

I’m not suggesting that IF is necessarily a panacea, many people are already doing great on more conventional meal plans. I am becoming more and more convinced, however, that a feast-famine eating pattern is a more natural one for humans than eating 6 to 8 small meals a day.

Even if you're not interested in the potential health gains, IF may be worth a try simply for a shift in routine – many find a break from constant, regular meal preparation a refreshing change.

* Ed Clements, creator of muscle-health-fitness.com, is an independent health and fitness writer who specialises in dietary, supplementation and weights training advice for improving body composition and hormone balance.


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