In recent years, many diet fads have inundated your senses and your sensibilities, all promising anything from miracle weight loss to helping you live forever. One of the most common questions I receive in my practice today involves Intermittent Fasting.
Intermittent fasting, which includes everything from periodic multiday fasts to skipping a meal or two on certain days of the week, may promote some of the same health benefits that uninterrupted calorie restriction promises. The idea of intermittent fasting is more palatable and accessible to most people because you don’t have to give up the idea of the “feast”, meaning you get to cut loose and have that second slice of pie. Multiple studies show that rodents that feast one day and fast the next often consume fewer calories overall than they would normally and live just as long as rats eating calorie-restricted meals every single day. Mark Mattson, head of the National Institute on Aging’s neuroscience laboratory, found in a 2003 study that mice that fasted regularly were healthier by some measures than mice subjected to continuous calorie restriction; they had lower levels of insulin and glucose in their blood, for example, which correlated to a decreased risk profile for development of Diabetes, showing increased insulin sensitivity and decreased blood glucose measurements.. Theoretically, this same benefit could be applied to people as well. Given that Diabetes is a national epidemic, as is obesity (which I feel has to do with increased insulin insensitivity), this merits a deeper look.
Even if calorie restriction does not help anyone live longer, a large portion of the data supports the idea that limiting food intake reduces the risks of diseases common in old age and lengthens the period of life spent in good health. If only one could claim those benefits without being hungry all the time. Well, there just might be a way. This is where Intermittent Fasting comes in.
Intermittent Fasting Explained
In its simplest form, Intermittent fasting (IF) is a term for an eating pattern that cycles between periods of fasting and eating.
It does not say anything about which foods you should eat, but rather when you should eat them.
In this respect, it is not a “diet” in the normal sense we are accustomed to . It is more accurately described as a “pattern of eating”. The most common methods involve daily 16 hour fasts, or fasting for 24 hours, twice per week (more on that later in this article).
Bottom Line: Intermittent fasting (IF) is a term for an eating pattern that cycles between periods of fasting and eating. It is currently very popular in the health and fitness community.
How to Do Intermittent Fasting
Intermittent fasting has been popular for a few years and many different methods exist.
All of them involve splitting into “eating periods” and “fasting periods.” During the fasting periods, you eat either very little or nothing at all.
The most popular methods include:
- The 16/8 Method: involves skipping breakfast and restricting your daily eating period to 8 hours, for example from 1 pm to 9 pm. Then you “fast” for 16 hours in between. This is the most popular method by far
- Eat-Stop-Eat: This involves fasting for 24 hours, once or twice a week, for example by not eating from dinner one day until dinner the next day. This is the hardest version for most people.
- The 5:2 Diet: On two non-consecutive days of the week, only eat 500-600 calories. Eat normally the other 5 days. By making you eat fewer calories, all of these methods should make you lose weight as long as you don’t compensate by eating much more during the eating periods.
I’ve personally tried all three and found the 16/8 method to be the easiest, most sustainable method.
Bottom Line: There are several different ways to do intermittent fasting. All of them split the day or week into “eating periods” and “fasting periods.”
How Intermittent Fasting Affects Your Cells and Hormones
When you fast, several things happen at the cellular and molecular level in your body. Hormone levels change, and cellular signals are altered.
Here are some changes that occur in your body when you fast:
- Human Growth Hormone (HGH): Growth hormone has been shown to increase substantially, leading to increased fat metabolism and muscle protein sysnthesis.
- Insulin: Insulin sensitivity significantly improve with a corresponding drop in insulin levels. This change makes stored body fat more accesible as an energy source for your body.
- Cellular repair: Cellular repair signals are triggered when fasting, allowing for healing of damaged cells
- Gene expression: There are changes in the function of genes related to longevity and protection against disease, specifically telomeres, which are the end caps to all of our genes that many in the scientific community link to againg
These changes in hormone levels, cell function and gene expression are responsible for the health benefits of intermittent fasting.
Bottom Line: When you fast, human growth hormone levels go up and insulin levels go down. Your body’s cells also change the expression of genes and initiate important cellular repair processes.
Health Benefits of Intermittent Fasting
Many studies have been done on intermittent fasting, in both animals and humans.
These studies have shown that it can have powerful benefits for weight control and the health of your body and brain. It may even help you live longer.
Here are the main health benefits of intermittent fasting:
- Weight loss: As mentioned above, intermittent fasting can help you lose weight and belly fat, without having to consciously restrict calories
- Insulin resistance: Intermittent fasting can reduce insulin resistance, lowering blood sugar by 3-6% and fasting insulin levels by 20-31% This should protect against type 2 diabetes.
- Inflammation: Some studies show reductions in markers of inflammation, a key driver of many chronic diseases Heart health: Intermittent fasting may reduce LDL cholesterol, blood triglycerides, inflammatory markers, blood sugar and insulin resistance. These are all risk factors for heart disease Cancer: Animal studies suggest that intermittent fasting may help prevent cancer Brain health: Intermittent fasting increases a brain hormone called BDNF, and may aid the growth of new nerve cells. It may also protect against Alzheimer’s disease
- Anti-aging: Intermittent fasting can extend lifespan in rats. Studies showed that fasted rats live as much as 36-83% longer Keep in mind that the research is still in its early stages. Many of the studies were small, short in duration or conducted in animals.
Safety and Side Effects
Hunger is the main side effect of intermittent fasting.
You may also feel weak and that your brain isn’t performing as well as you’re used to.
This may only be temporary, as it can take some time for your body to adapt to the new meal schedule.
If you have a medical condition, then you should consult with your doctor before trying intermittent fasting.
This is particularly important if you:
- Have diabetes.
- Have problems with blood sugar regulation.
- Have low blood pressure.
- Take medications.
- Are underweight.
- Have a history of eating disorders.
- Are a female who is trying to conceive.
- Are a female with a history of amenorrhea.
- Are pregnant or breastfeeding.
All that being said, intermittent fasting does have an outstanding safety profile. There is nothing “dangerous” about not eating for a while if you are healthy and well nourished overall.
Bottom Line: The most common side effect of intermittent fasting is hunger. People with certain medical conditions should not fast without consulting with a doctor first.
Frequently Asked Questions
- Can I drink liquids during the fast?
Yes. Water, coffee, tea and other non-caloric beverages are fine. Do not add sugar to your coffee. Small amounts of milk or cream may be okay.
Coffee can be particularly beneficial during a fast, because it can blunt hunger.
- Isn’t it unhealthy to skip breakfast?
People associate skipping breakfast with eating more and unhealthier. As long as you make sure to eat healthy food for the rest of the day and keep your portions under control, it will work well.
- Can I take supplements while fasting?
Yes. However, keep in mind that some supplements (like fat-soluble vitamins) may work better when taken with meals.
- Can I work out while fasted?
Yes, fasted workouts are fine. Some people recommend taking branched-chain amino acids (BCAAs) before a fasted workout.
- Will fasting cause muscle loss?
All weight loss methods can cause muscle loss, that is why it is important to lift weights and keep protein intake high. One study shows that intermittent fasting causes less muscle loss than regular calorie restriction.
- Will fasting slow down my metabolism?
No. Studies show that short-term fasts actually boost metabolism (14, 15). However, longer fasts (3 days or more) can suppress metabolism (36).
- Should kids fast?
That’s probably a bad idea.