What is intermittent fasting? Does it have any real health benefits?
What is intermittent fasting?
Intermittent fasting is when you alternate between periods of eating and fasting. It doesn’t specify which foods you should eat but rather when you should eat them. In this respect, it’s not a diet in the conventional sense but more accurately described as an eating pattern.
Fasting has been a practice throughout human evolution. Ancient hunter-gatherers didn’t have supermarkets, refrigerators or food available year-round. Sometimes they couldn’t find anything to eat.
As a result, humans evolved to be able to function without food for extended periods of time.
In fact, fasting from time to time is more natural than always eating 3–4 (or more) meals per day.
Fasting is also often done for religious or spiritual reasons, including in Islam, Christianity, Judaism and Buddhism.
Fasting for a certain number of hours each day or eating just one meal a couple days a week, can help your body burn fat. And scientific evidence points to some health benefits, as well.
Intermittent fasting methods
There are many ways to fast and to reap the underlying benefits of going for some time without calories.
Common intermittent fasting schedules include:
This involves consuming all of your meals within a period of 4-12 hours in a day. For example, you could choose to have your meals and calories between 8 am and 6 pm. Limiting your calorie intake to daylight hours is called “eating with the sun”. Time-restricted eating is particularly beneficial if you eat your meals before sunset. Not only does this help you eliminate bad habits like late-night snacking, but it improves your sleep and blood sugar control. Over time, time-restricted eating can lower your blood sugar levels, make you more sensitive to insulin, and reduce your blood pressure.
This involves packing all of your day’s calories in a single meal that you consume within 1-2 hours. A small study showed that fasting for 24 hours 3 times a week and eating only dinner on fasting days, eliminated the need for insulin in type-2 diabetes patients. This fasting approach also resulted in improved HbA1C, lower body mass index, and reduced waist circumference.
Alternate-day Fasting (ADF)
This involves alternating between days in which you consume no calories and days in which you eat normally. Another way of looking at ADF is as three 36-hour fasts per week. For example, eat normally on Monday until 6pm. Don’t eat until breakfast on Wednesday morning. Finish dinner by around 6pm Wednesday night. Now don’t eat again until breakfast on Friday. Eat normally the rest of the day and finish dinner by 6pm or so Friday night. Now don’t eat again until breakfast on Sunday. This way of fasting increases life span in rodents by 80%, possibly by decreasing glucose levels and regulating insulin. It also reduces the incidence of cancer in lab animals genetically predisposed to it. Alternate-day fasting is the most studied method of fasting in humans, and it’s been shown to lead to weight loss and reduce circulating levels of LDL or ‘bad’ cholesterol.
The 5:2 diet
This involves fasting for two days per week, either consecutively or non-consecutively, and eating normally the rest of the week. For example, you might decide to fast Monday and Tuesday and then eat normally the rest of the week. You can also look at it as one 60-hour fast per week. Finish dinner at 6pm on Sunday night and don’t eat again until breakfast on Wednesday morning, for example.
Prolonged fasting for 3-5 days
This involves going with no calories for 3-5 days. These types of fasts are usually done under medical supervision. All studies of prolonged fasting allow up to 500 calories during fasting days. These calories should come from low-protein, low-carb foods. This usually means vegetable juices and vegetable soup, averaging a total calorie intake of 200–250 kcal and 25–35 g of carbohydrates per day
Traditional fasts typically last anywhere from 24 hours to seven days or longer. They emphasize developing willpower and honing self-discipline as opposed to weight loss, making them a favorite among those looking for a mental or spiritual refresh. While you’ll certainly see some physical effects, the changes of a single fast won’t be permanent. That said, it’s a useful tool to help you understand hunger and your reaction to it.
The Science of Fasting
When you fast, your body stops using glucose for fuel and starts to metabolize fat. This helps drive blood sugar and insulin levels down, reducing your likelihood of gaining weight and developing diabetes or heart disease. Intermittent fasting also increases the release of human growth hormone, which regulates your metabolism and preserves muscle mass while burning fat.
Beneficial neurochemical changes in the brain can occur as well when you fast for short periods of time. Intermittent fasting can lead to improved concentration, better memory and even boosted energy levels.
Intermittent fasting increases the production of a protein in the brain called brain-derived neurotrophic factor, which stimulates the production of new neurons in the brain. Neurons transmit and receive information, so having more of them improves your memory and ability to learn.
People also report having more energy when they fast due to improved mitochondrial function. Studies show that intermittent fasting stimulates the production of ketones, which act as an energy source for neurons. Upon the release of these ketones our bodies increase the number of mitochondria in our neurons, which are responsible for taking in nutrients and creating energy. The result: a brain and body that’s more capable of producing energy and burning fat.
Safety and Side Effects
Hunger is the main side effect of intermittent fasting.
You may also feel weak and your brain may not perform 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, you should consult with your doctor before trying intermittent fasting.
This is particularly important if you:
Have problems with blood sugar regulation.
Have low blood pressure.
Have a history of eating disorders.
Are a woman who is trying to conceive.
Are a woman with a history of amenorrhea.
Are pregnant or breastfeeding.
Some general safety tips
Drink water when you are thirsty.
Adjust your caloric intake during your feeding windows so that you consume enough calories to meet your energy needs according to your weight goals.
If you feel faint, dizzy or nauseous, we recommend breaking your fast early and speaking with your primary care physician. You may have symptoms of low blood sugar or another issue.
Talk to your physician before upping your fasting window beyond 18 hours per day.
Break your fast (especially fasts of over 24 hours) with low glycemic index foods, such as lean protein and healthy fats like avocados
Never do fasts longer than 2 days by yourself. Always tell someone, a family member or friend (in addition to your physician) and keep them updated on how you are feeling as you progress.
During fasts longer than 2 days, watch for signs of electrolyte imbalance: muscle spasms, weakness, blood pressure changes, irregular heartbeat, numbness and confusion.
The benefits of intermittent fasting
Although weight loss is one of the most obvious benefits of intermittent fasting, it definitely isn’t a crazy fad diet. Quite the opposite, it can be a sustainable strategy for people wanting to achieve gradual weight loss and maintain a healthy weight.
Essentially, intermittent fasting kickstarts the fat-burning state of ketosis. While you fast, your body burns through its glucose reserves for energy, then it begins to burn fat for fuel.
Improved insulin sensitivity and lower blood pressure
A study conducted by researchers from the University of Alabama with a small group of obese men with prediabetes showed the benefits of fasting on insulin and blood pressure. The group ate during an 8 hour time period early in the day (7am - 3pm) and fasted after 3pm.
The results showed dramatically lower insulin levels and significantly improved insulin sensitivity, as well as significantly lower blood pressure.
May boost the human growth hormone (HGH)
Human growth hormone (HGH) is produced by your pituitary gland and plays a key role in growth, cell repair, metabolism, and body composition.
When your levels of HGH are low, the risk of disease and gaining weight are increased.
Intermittent fasting helps optimize your HGH levels which in turn increased availability of fats and affects how they’re used for energy. This important hormone also helps preserve muscle mass and bone density.
Can support brain health
Intermittent fasting improves energy production, oxygen radical metabolism, and cellular stress responses in ways that help guard brain cells against environmental and genetic stressors as we age.
Intermittent fasting may help fight chronic inflammation
Chronic inflammation - when your body is in a constant state of inflammation - can wreak havoc on your health and trigger diseases including heart disease and diabetes.
A poor diet of fried, sugary and fatty foods plus lifestyle factors like smoking and stress contribute to chronic inflammation.
Studies have shown that intermittent fasting may bring about an anti-inflammatory effect which can reduce the risk of heart disease and diabetes and even improve asthma.
Cuts down on time for meal prep and eating
If you’ve got a busy schedule you might find the time-saving aspect of intermittent fasting a bonus benefit!
Some intermittent fasting advocates even say it helps them reduce their food budget too; eating less means less trips to the grocery store.
So there you go, intermittent fasting could even benefit your productivity and bank account balance!
Intermittent fasting can be an effective tool for improving your health and losing weight. But it’s essential to consider all the benefits and disadvantages of intermittent fasting before giving it a go. It's important to try methods that make you happy and don’t cause your mind and body harm. If you’re not sure it’s for you or don’t know where to start, chat with your healthcare provider about which eating plan might suit you best and what red flags to watch out for as you get started.