Ask the Pharmacist

Q) I have heard a lot about intermittent fasting over the years. What is it exactly and does it work?

A) Before we look at the science around the benefits and possible risks associated with intermittent fasting, we should first talk about just what it is which is a subject unto itself. In general, intermittent fasting is a dieting strategy that involves alternating periods of food consumption with longer than is typical periods of fasting. Within this broad category, there are multiple subtypes some of which have been studied more extensively than others.

These include:

· Time-restricted eating- involves fasting every day, usually for 14 to 18 hours. You therefore eat your 2 to 3 meals in the remaining 6 to 10 hours of the day.
· The 5:2 diet- you eat normally for 5 days of the week and restrict your calories to 500-600 on the remaining non consecutive 2 days.
· Alternate day fasting- which is self-explanatory
· The warrior diet- eat small amounts of raw fruits and vegetables throughout the day and eat one large meal at night.

Water, coffee and other calorie-free beverages are allowed during the fasts with any of these options. These intermittent fasting diets can obviously be challenging to adhere to and are definitely not for everyone.

People with diabetes and a few other disease states should only do this type of dieting while under clinical supervision. It is also contraindicated (i.e. strongly discouraged) in children under the age of 12 and in those with a history of eating disorders. Opinions vary on whether it is an acceptable strategy in obese adolescents or adults over the age of 70 where its safety has not been studied and there are concerns it may increase the rate of age-related muscle loss.

There are also some potential side effects you may experience on your fasting days. Headaches may occur during the first few weeks and not surprisingly, you are likely to feel hungry especially in the early stages of your diet. Some have reported their moods to be more mercurial and others have complained of constipation, fatigue and sleep disturbances.

However, the data from assorted trials did not support any of these from being more common in people who are fasting versus those who are not with the exception of the headaches. It is also worth noting that while many were concerned they would feel weak or not be able to concentrate well during the fast, evidence indicates that the ability to focus often seems to be enhanced.

So, just how effective is fasting? Well, it should work based on the science supporting it. Our liver normally stores glucose (sugar) which our body uses preferentially to meet our energy needs. In general, it takes about to 10 to 12 hours to use up the glucose stored in the liver after which the body will start to break down fat to fuel our requirements. Hence fasting should lead to decreased fat and weight loss.

In the relatively few studies looking at intermittent fasting, it was found that all three of the main methods (the exception being the warrior diet as it has not been studied as extensively can produce a 3 to 8% weight loss over an 8 to 12 week period. Those numbers are significant but not any different than what is produced with a calorie restricted diet.

Some studies (but not all) have found that blood pressure, cholesterol, triglycerides, insulin resistance and blood sugars have improved as well but this good news should be tempered by the fact that the studies were short (so we don’t know for sure if the positive effects will last) and in small numbers of participants (which may lead to inaccuracies in our results). Still this does look promising and safe for most of us to try if we are so inclined. Advice for those who wish to pursue this include to eating at least 50gm of lean protein on fasting days to help control hunger and prevent the loss of lean mass.

  • Make sure you include fruits, vegetables and whole grains to increase your fibre as studies have revealed that many of these diets are quite low in it.
  • Make sure you maintain your fluid requirements (9 cups for women, 12 for men) to help prevent headaches.

The timing of when you eat may matter as well. A recent study published in JAMA concluded that time-restricted eating was ineffective for losing weight and improving measurements of health but the participants were only slowed to eat from 12p.m. to 8 p.m.. There is a growing evidence that suggests that muscle growth & repair is somewhat regulated by our body’s circadian rhythms (i.e. our body’s clock so to speak). Our bodies seem to be better able to metabolize food earlier in the day and hence the same number of calories may lead to less weight gain if consumed then. As well eating protein in the morning may be more beneficial for maintaining muscle mass and strength.

The take-away is that if your schedule allows it, you should target your fasting period to coincide with typical breakfast times. In short, there look there are likely health benefits to intermittent fasting but the long-term effects are unknown and those benefits do not look a whole lot different than those seen by other weight loss type diets. For more information about this or any other health related requests, contact your pharmacist.