Intermittent Fasting 16/8: A Simple Beginner’s Guide
Written and Medically Reviewed by Ana Reisdorf, MS, RD on January 23, 2020.
Intermittent fasting 16/8 is a style of fasting which has become popular in recent years. In this article, you’re going to learn what 16/8 IF fasting is, the pros and cons, as well as how you can integrate fasting into your current schedule.
What Is Intermittent Fasting 16/8?
Intermittent fasting is a form of time-restricted eating. There is a “fasting” and a “feeding” period. During the fasting period, you don’t eat, and during the feeding period, you eat all of your food for the day.
There are different styles of intermittent fasting, which are primarily differentiated based on the hours of each fasting and feeding period. Intermittent fasting 16/8 requires 16 hours of fasting and 8 hours of feeding, hence “16/8”.
7 Benefits Of IF 16/8
Fasting for any prolonged period induces a state of “ketosis” in the body, otherwise known as fat burning. By abstaining from consuming food, your body runs out of glycogen (stored sugar) in the liver and is forced to begin burning fat (1,2).
The body produces the “ketones” acetone, acetoacetate, and beta-hydroxybutyrate (BHB) when it’s in a state of ketosis. These ketones supply the body and brain with energy when food is absent, and it is this energy source that we relied on thousands of years ago during periods of food scarcity.
Sixteen hours daily isn’t long enough to enter a very deep state of ketosis, but it is long enough that you will experience some of the health benefits associated with ketosis, such as:
1. Increased growth hormone
Research has shown that short-term intermittent fasting can increase growth hormone (GH) levels five-fold (3) . Higher levels of GH are required during a fasting period for several reasons, such as increasing energy availability, and preserving muscle mass. Higher growth hormone levels are positively associated with decreased aging, increased muscle mass, strength, and a lower body fat percentage (4, 5).
2. Increased autophagy
Intermittent fasting and especially prolonged fasting has been shown to induce autophagy (6). Autophagy essentially causes cells to recycle themselves by removing unnecessary waste. You can read more about autophagy here.
3. Beneficial for Type 2 diabetes
Type 2 diabetes is a metabolic disease characterized by insulin resistance. Insulin is a hormone released from beta cells in the pancreas. When a person consumes food, particularly carbohydrates, there is an increase in blood sugar as food digests.
Insulin takes sugar from the blood (blood glucose) and transports it to areas of the body which require it, such as the brain. Insulin resistance is when the body has a dysfunctional response to insulin. The body becomes less effective at moving sugar from the blood to areas such as the brain. This leads to chronically high blood sugar levels.
Studies carried out on humans have shown that intermittent fasting decreases fasting blood sugar by 3-6%, and decreases insulin by 20-31% (7). IF 16/8, in particular, is excellent for type 2 diabetics as it’s incredibly sustainable and easy to follow.
Fasting can also help with weight loss, which further helps to ameliorate typical traits of metabolic disease. If you have diabetes, be sure to speak with your doctor prior to beginning 16/8 to ensure it’s right for you.
4. Reduced oxidative stress
The body naturally produces something called “free radicals.” Free radicals are natural byproducts of human metabolism. However, excessive free radicals are toxic to the body and can cause damage to cells and tissue through a process called oxidative stress. Studies have shown intermittent fasting may be able to improve the body’s resistance to oxidative stress (8, 9).
Oxidative stress speeds up aging and is also associated with the onset of numerous chronic diseases. Antioxidants, which we get by consuming various fruits and vegetables, counteract oxidative damage and help to prevent free radical damage to our cells, proteins, and DNA.
5. Improved cardiovascular health
Heart disease is one of the leading causes of death in the world (10). Various health markers such as LDL cholesterol levels, blood pressure, triglyceride levels, inflammatory markers, and blood sugar levels are all major risk factors medical professionals use to predict and diagnosis one’s risk of heart disease. For example, high triglyceride levels (fat in the blood) is strongly associated with an increased risk of heart disease. Intermittent fasting has been shown to improve many of these risk factors in various studies (11, 12, 13).
However, more research does need to be done to determine whether it is intermittent fasting or caloric restriction which actually improves these risk factors. Intermittent fasting can help to promote weight loss. Losing weight can also help to reduce triglyceride levels. And so this makes it difficult for researchers to discern whether it is intermittent fasting per se or weight loss as a consequence of meal timing, which improves heart disease risk factors.
6. Improved cognitive health
Emerging research is showing that intermittent fasting may actually help improve brain health.
One study carried out on rats showed that intermittent fasting was able to increase the growth of new nerve cells, which are beneficial for brain health (14).
Research has also shown that intermittent fasting increases brain-derived neurotrophic factor (BDNF) (15). BDNF is a protein which upregulates the production of brain cells, a process known as neurogenesis. BDNF improves the integrity and maturation of nerve cells.
Lower BDNF levels have been suggested to play a significant role in the pathophysiology of depression (16). This may imply that increasing BDNF through intermittent fasting could help ameliorate symptoms of depression. However, depression is very complex, and we don’t have any clinical trials yet to make this sort of claim.
7. Increased fat loss
Most people who are interested in trying 16/8 intermittent fasting are likely doing it for weight loss, which isn’t surprising as intermittent fasting is extremely effective for fat loss.
The question is, why is intermittent fasting so effective for weight loss?
Intermittent fasting increases growth hormone levels, decreases insulin levels and increases hormones such as norepinephrine which aid the body in breaking down fat for energy. Prolonged fasting has also been shown to increase people’s metabolic rate by 3.6-14% according to some research, primarily due to an increase in stress hormones (17, 18).
However, most quality research has made it clear that intermittent fasting is effective for weight loss primarily because it helps people eat less food. Multiple meta-analyses have confirmed this (19, 20).
Intermittent fasting decreases food intake in two ways:
Reduced time to eat
If you only have 8 hours to eat your food daily, you will probably eat less food throughout your day. If you eat less food, you eat fewer calories. Fewer total calories equal a greater chance of achieving a consistent caloric deficit, which drives fat loss.
Many people paradoxically report decreased hunger levels while intermittent fasting. Decreased hunger leads to less overall calorie intake, which leads to greater weight loss. There may also be a physiological explanation for decreased hunger from intermittent fasting. Fasting increases ketones, which have been shown to reduce ghrelin, known as the “hunger hormone”. The decrease in ghrelin from fasting could decrease appetite and therefore help to speed up weight loss (21, 22, 23 ).
What Are The Downsides of 16/8?
A systematic review of intermittent fasting studies with trial periods of at least six months concluded that there are some minor physical symptoms experienced by some people practicing intermittent fasting 24.
These side effects included:
- Decreased body temperature
- Difficulty waking and falling asleep
- Feeling cold
- Dry skin
- Lowered libido
- Low blood sugar levels
Keep in mind that some of these symptoms are due to undereating food, rather than intermittent fasting itself.
Since intermittent fasting is so effective at controlling food intake, some people tend to undereat. Undereating can cause symptoms such as feeling cold due to a downregulation of thyroid function. Be sure to eat enough food during your feeding period to minimize side effects.
Who Should Not Do It?
Pregnant and breastfeeding mothers
Pregnancy and breastfeeding require a larger calorie intake. It’s not recommended that a pregnant or breastfeeding woman practices intermittent fasting unless it’s recommended to them by their medical professional.
Intermittent fasting is a stress on the body. Increased stress in response to the absence of food is normal. One of the reasons intermittent fasting is beneficial is because it’s stressful, similar to how exercise is beneficial. The stress of exercise is stressful for the body, but the body later recovers and becomes more resilient to that stress. Fasting works in a similar way. This adaptive stress response is called hormesis.
However, too much stress, especially for stress-sensitive people, can be harmful. Intermittent fasting increases stress hormones such as cortisol and adrenaline. Increased stress hormones can boost energy levels, but over time, chronic stress can be detrimental. If you’re already stressed for other reasons, then adding intermittent fasting into your lifestyle could make things worse.
Go ahead and try intermittent fasting, but please start slow if you’re sensitive to stress.
People with eating disorders
Although intermittent fasting is a healthy practice, fasting can become another form of abuse for people with eating disorders. People with eating disorders such as anorexia should stay clear from any diet practice which promotes caloric restriction.
How To Do 16/8 Intermittent Fasting
Most people tend to eat their calories from 12-8 pm or 1-9 pm. These hours are popular as this makes 16/8 fasting easy to fit into a 9-5 pm work schedule. Feel free to change these hours to suit your own schedule.
The first few weeks of any intermittent fasting protocol are the most difficult. Most people have formed a habit of continuously eating throughout the day for most of their lives. Suddenly changing this routine can be a challenging adjustment to make.
You may find that you’re hungry the first day you try to skip breakfast. Don’t worry. This is normal. Stay committed to intermittent fasting for at least two weeks before you make a decision as to whether it’s right for you. Two weeks should give your body and mind plenty of time to adjust.
If you’re still struggling, here are some measures you can take to make the transition easier:
You can begin with a twelve or fourteen hour fast in the first week, and transition into sixteen hours in the second week.
Don’t ignore your diet
16/8 intermittent fasting will help you lose weight and improve your health. But this doesn’t mean fasting is an excuse to eat whatever you want. An unhealthy diet will result in poor health and difficulty losing weight, regardless of whether you’re doing 16/8 intermittent fasting. Ensure that you’re eating a diet abundant in high-quality protein sources, healthy fats, and complex carbohydrates.
What can you eat during your 16/8 fasting period?
You can eat and drink the following during your fasting window:
- Sugar-free gum
- Any zero calorie drink
Adding a splash of milk in your coffee or tea is fine as long you keep it under 10-20 calories.
Intermittent fasting has a number of potential health benefits and is especially effective for people trying to lose weight.
16/8 intermittent fasting seems to be especially popular for beginners due to how easy it is to follow.