Intermittent fasting is the hot new diet on the wellness circuit, and I’ve already received a lot of inquiries about it. So I figured I’d write down my thoughts to share with you all.
For those who are not familiar, there are several types of intermittent fasting, two of which are most popular.
One version restricts eating to an 8 hour window of your day. (So if you eat breakfast at 8am, you should be done with all of your meals and snacks by 4pm.) With this version, you are not necessarily told what or how much to eat, just when.
The other version is known as the 5:2. This allows normal eating 5 days a week and severely restricts caloric intake during the other 2. (Severe calorie restriction is 25% of normal intake, which they say comes to 500 calories for women and 600 calories for men.)
Now why is this diet getting so much attention? Let’s see what all the fuss is about…
Proponents of intermittent fasting claim that it can do the following:
1. Improve insulin sensitivity and blood sugar levels.
In a typical feeding state, our bodies turn food into glucose (AKA sugar). That glucose gets absorbed into the blood. Insulin is then released to help cells take in glucose where it is used for energy.
But when our bodies are in a prolonged feeding state (read: overloaded with food), the body can’t keep up with all the glucose in the blood. It tries to pump insulin out to help the cells absorb it, but at a certain point, the body just stops responding. This is known as “insulin resistance.”
If we become insulin resistant, when we eat, our blood sugar rises and we have a hard time bringing it back down. This often causes pre-diabetes, and if not resolved, can eventually turn into Type 2 Diabetes.
Enter intermittent fasting. By restricting food intake for extended periods of time, the body gets a reprieve from constantly digesting food and having to figure out how to deal with all the glucose in the blood. This allows us to recalibrate our bodies’ sensitivity to insulin and regain control of our blood glucose levels.
2. Increase longevity.
We are familiar with mental and emotional stress, which can take a toll on the mind. But there is also physical stress, which can wreak havoc on the body. Toxins in the atmosphere, carcinogens, and even the byproducts of certain bodily functions put stress on our bodies. The cumulation of these stressors can cause our bodies to breakdown or malfunction. And the prevention of these stressors can potentially help us live longer.
It may come as a surprise, but food digestion produces byproducts that cause physical stress on the body. It is a necessary evil. We need food to survive, and yet digesting that food produces harmful materials. It is possible that because of this, certain intermittent fasting has been shown to help reduce the amount of stress on our cells and may therefore help us live longer.
However, this is more likely due to the reduction in overall food intake than it is due to the timing of the food intake. So if the intermittent fasting does not actually reduce the amount of food your body needs to digest, it may not make a difference at all to longevity.
3. Protect the brain.
By restricting food intake for an extended period of time, our bodies run out of glucose, which is the body’s preferred source of energy. When that happens, we start to use fat as fuel, producing ketones as a byproduct. (Yes, the same ketones they’re all talking about in the Ketogenic Diet.) And ketones have been shown to have certain neurological benefits, specifically with seizure control for those suffering from epilepsy.
4. Help with weight loss.
Because intermittent fasting restricts when you can eat, it is often correlated with calorie restriction and can often result in weight loss. However, if the intermittent fasting does not actually reduce the amount of calories you are consuming, it will likely not make a difference to the scale.
5. Boost metabolism.
By containing your eating hours to the first part of the day, you are aligning your intake with your circadian rhythm. When we wake up and haven’t eaten for a while, our bodies are better equipped to respond to food, break it down, and use it for energy. This can help optimize metabolism. However, if you choose to contain your eating to the later hours of the day, you may actually be hurting your metabolism.
Now it’s time for the caveat.
The research out there is very limited. Most of the studies that have been done are smaller scale studies spanning shorter periods of time, so the strength of the evidence is lacking. Furthermore, most of the studies do not involve humans, so it is difficult to apply those findings to the human species with total conviction. Once more research is done, we will have a better sense of whether intermittent fasting is in fact the better way to eat.
But let’s say you still wanted to try it. As a dietitian, here are my precautions...
1. Do not expect to lose weight if you are not cutting back on your total intake.
Having unrealistic expectations for a diet can lead to feelings of defeat and self-doubt. Therefore, it is important to recognize that while there may be health benefits to intermittent fasting aside from weight loss, you should not expect to lose weight if you are simply condensing your normal diet into an 8 hour window. It has nothing to do with you. It is just plain science and math.
2. Avoid binge-eating.
Oftentimes going longer periods without food can lead to food fantasies and an urge to ultimately eat more than you normally would once you start eating again. Binge eating is never healthy and can even lead to weight gain, so if that becomes a by-product of intermittent fasting, then intermittent fasting is definitely not for you.
3. Do not reserve your eating hours to night-time.
As I mentioned earlier, intermittent fasting can be good for your metabolism when your eating hours are earlier in the day. However, reserving your intake for later in the day can actually be detrimental to your circadian rhythm and metabolism. During sleep, our bodies are in rest and recovery mode, so loading our intake on the back-end of the day can disrupt that.
4. Intermittent fasting can be dangerous for certain populations.
- Diabetics on insulin.
While intermittent fasting may help a pre-diabetic or a diabetic who is not insulin-dependent by restoring insulin sensitivity and reducing blood sugar levels, it can be very dangerous for diabetics who rely on insulin injections to control their blood sugar. This is because insulin doses are often aligned with typical eating habits. If you are on insulin and suddenly drastically change your eating habits without changing your insulin accordingly, it can cause Diabetic Ketoacidosis, which when left untreated can be fatal.
- Pregnant women.
When you are pregnant, you are not only eating for yourself, you are eating for the growing baby inside you. As such, adopting new drastic eating behaviors can be a bad idea during pregnancy.
- People taking certain medications.
Some medications must be taken with food. If you are on a regimen that requires you to eat when taking your medications, it is important to follow your regimen and not compromise your health by fasting.
- People with a history of eating disorders.
Because intermittent fasting promotes rigidity and going a long time without eating, these can be triggers for people who are recovering from an eating disorder.
The bottom line:
Ultimately, I think having a finite “stop time” to our eating can be helpful as we tend to do more of our mindless snacking and/or less inhibited eating at night; however as with any “diet” there are usually pitfalls to watch out for. Defining your wellness goals; identifying healthy, realistic, and concrete steps to make those goals a reality; and regularly monitoring your progress is truly the best way to create lasting change. And having a dietitian to help along the way doesn’t hurt either!