Intermittent fasting has risen in popularity due to numerous studies showing it has powerful effects on weight loss, blood sugar balancing and heart health. Common fasting methods involve daily 16-hour fasts, or fasting for 24 hours, twice per week. Intermittent fasting is nothing new—our hunter gatherer ancestors would fast when food was scarce and some people fast for religious reasons. In fact, once a year, Muslims observe Ramadan, a month of fasting from dawn until sunset.
What is intermittent fasting?
Intermittent fasting is a term used to describe a pattern of eating that cycles between periods of eating and fasting. It does not refer to what you should eat, but rather when you should eat. There are many different variations of intermittent fasting that are used around the world. Here are some examples:
- Alternate day fasting—eat every second day to achieve your health goals. On fast days either don’t eat or restrict calorie intake to a maximum 500.
- The 5:2 diet—on two non-consecutive days of the week consume 500-600 calories. Eat normally on the remaining 5 days.
- The 16/8 method—skip breakfast and restrict your daily eating period to 8 hours during the day, for example from 12pm-8pm. This diet, also called the Leangains protocols, involves 16 hours of fasting in between eating.
- The warrior diet—eat light meals of fruit and vegetables during the day and eat a large meal at night.
- Eat-stop-eat—pick 1-2 days a week where you fast for 24 hours. For example, you fast from lunch one day until lunch the next day.
The benefits of intermittent fasting
The mechanisms by which intermittent fasting improves health and counteracts disease processes involve activation of adaptive cellular stress response signalling pathways that initiate important cellular repair processes and change the expression of genes that relate to longevity and protect against disease. In doing so it also achieves the following benefits:
Weight loss
The main benefit of intermittent fasting is weight loss. Provided you don’t “pig out” on your eating days, most people find it a straightforward way to lose weight. By eating fewer meals you are automatically eating less calories which facilitates weight loss and fat-burning. If you don’t have a constant intake of food your body will find alternate sources of energy such as fat stores. In addition to this, fasting improves levels of hormones such as insulin, growth hormone, noradrenaline and leptin. Due to the changes in these hormones short-term fasting may increase your metabolic rate by 3.6-14% and body weight by 3-7%.
A study that focused on the 16/8 method of intermittent fasting showed that it significantly reduced fat mass while retaining both muscle mass and strength. This is one reason why the 16/8 method of intermittent fasting is the most popular, and it does seem easier to follow than other fasting diets.
Heart health
Having your weight in the healthy weight range is beneficial to your heart. However, there are lots of other benefits of intermittent fasting for our cardiovascular system by reducing disease risk factors. Whole-day fasting trials lasting 12-24 weeks found a reduction in total cholesterol by 5-20% and triglycerides by 17-50%. Having elevated levels of cholesterol and triglycerides can contribute to the development of heart disease.
One animal study showed that intermittent fasting caused an increase in levels of adiponectin which is a protein involved in the metabolism of fat and sugar that may be protective against heart disease. In fact, in one study, rats who fasted every other day were nearly 66 % more likely to survive a heart attack than those on a normal diet.
Reduce insulin levels
Intermittent fasting has many benefits for diabetics and those with insulin resistance by having a positive effect on blood sugars. When we eat carbohydrates, insulin is released to help transport sugar from our bloodstream into cells for energy. When you fast for regular intervals insulin levels drop which makes stored body fat more accessible. Insulin doesn’t always work well when you have diabetes and intermittent fasting changes this by making insulin more efficient and our cells more sensitive to its effects. One study showed that fasting decreased blood sugar by 12 % and lowered insulin levels by nearly 53 %.
Brain power
Unfortunately, studies on intermittent fasting and its effect on brain health have only been conducted on animals. But here is what researchers found:
- enhanced cognitive function
- protection against changes in memory and learning function
- aids in the growth of new nerve cells
- it may also slow the progression of Alzheimer’s disease
As a result of all the above benefits intermittent fasting promotes longevity and provides protection against inflammation, cancer and chronic disease
Precautions
In some cases, intermittent fasting may be harmful. If you are underweight, or suffer from an eating disorder this way of dieting isn’t advised. Women who are pregnant, breastfeeding or even trying to conceive should avoid fasting periods. There is also some evidence that intermittent fasting may not be as beneficial for females when compared to males by actually worsening blood sugar control. In animal studies intermittent fasting may lead to infertility, missed menstrual cycles and emaciation. If you have a medical condition or take medications, then it is important you consult with your doctor first before trying intermittent fasting.
References
- Tinsley GM, La Bounty PM. Effects of intermittent fasting on body composition and clinical health markers in humans. Nutr Rev. 2015 Oct;73(10):661-74 https://www.ncbi.nlm.nih.gov/pubmed/26374764
- Wan R, Ahmet I, Brown M, Cheng A, Kamimura N, Talan M, Mattson MP. Cardioprotective effect of intermittent fasting is associated with an elevation of adiponectin levels in rats. J Nutr Biochem. 2010 May;21(5):413-7 https://www.ncbi.nlm.nih.gov/pubmed/19423320/
- Katare RG, Kakinuma Y, Arikawa M, Yamasaki F, Sato T. Chronic intermittent fasting improves the survival following large myocardial ischemia by activation of BDNF/VEGF/PI3K signalling pathway. J Mol Cell Cardiol. 2009 Mar;46(3):405-12 https://www.ncbi.nlm.nih.gov/pubmed/19059263/
- Mattson MP, Longo VD, Harvie M. Impact of intermittent fasting on health and disease processes. Ageing Res Rev. 2017 Oct;39:46-58 https://www.ncbi.nlm.nih.gov/pubmed/27810402
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