Intermittent fasting (also referred to as IF) may just seem like the latest diet trend, but fasting actually has a long history of use by both humans and animals. Before we had access to food all day every day, our bodies adapted to going long periods of time without food. Instinctively, humans and animals use fasting when they’re sick and it has long been used as a spiritual and religious practice.
The majority of the initial research supporting IF was on animal studies, but now, more and more research on humans is showing that IF continues to have a wide range of benefits, so much so that I felt it was worth addressing in a post.
IF is when you go prolonged periods without eating. There are many different ways to fast, as well as variation in the length of fasts. The main idea is that you have hours or days where you eat, and ones when you don’t eat at all.
The most common fasting routines are:
It might seem crazy to go such long periods without eating but remember that for many of the hours you’re fasting you’re already asleep. You may have been engaging in a relaxed form of IF without realizing it if, say, you stop eating at 8pm and don’t eat until after 8am. That’s a 12 hour fast.
One thing to note is that IF is more of an eating pattern than a diet, because there aren’t any guidelines on what to eat and not to eat. The great thing about IF is that it can be adjusted to best suit your lifestyle and needs and there’s actually research to support many different variations. For example, a recent study on pre-diabetic men found that the men experienced greater improvements in insulin sensitivity, oxidative stress and appetite when their eating window was earlier and they stopped eating by 3pm.
Recent research has shown IF to improve biomarkers of disease, reduce oxidative stress and preserve learning and memory functioning. The benefits may also include increased insulin sensitivity, weight loss, reduced inflammation and lowered risk of heart disease.
There are several theories about why fasting is so beneficial. The main theory is that during the fasting period, cells are under a mild stress. While excessive and prolonged stress can be bad for your health, some stresses, like fasting or vigorous exercise for example, can be very beneficial because the cells respond by adapting to enhance their ability to cope with stress and potentially resist disease. When you’re fasted, your cells also initiate cellular repair and undergo something called autophagy, where they remove old and dysfunctional proteins that build up inside cells.
When combined with a well balanced and nutritious diet, it can also promote weight loss. There is of course the logic that when you reduce the amount of hours you have to eat, you’ll likely eat less and therefore lose weight. But when you don’t eat your insulin levels also drop dramatically, which enables your body to start to burn stored fat for energy instead of food.
IF isn’t for everyone. Women should be extra careful when attempting it because the hormones regulating key functions like ovulation are incredibly sensitive to your energy intake. It’s also not recommended for pregnant or lactating women or someone with weakened immunity. IF is not recommended for someone who has a history of disordered eating or struggles with binge eating. Lastly, it should not be attempted by someone with any pre-existing health condition such as diabetes, heart disease or a thyroid disorder, except under the direction of a healthcare professional.
Before getting pregnant, I tried intermittent fasting for a short period of time. I stopped eating by 7pm and didn’t eat again until 10am or 11am, depending how long I could make it. I found it incredibly difficult and did not feel better doing it. I believe that this is due to the different effects IF can have on men vs women and the stress response it can elicit on women. I have always eaten really shortly after waking up, or at least within an hour, and simply feel better that way. Interestingly, I have had success with clients implementing IF for weight-loss and cravings, so I think this just goes to show there is no one diet or way of eating that works for everyone.
Natalia, one of the nutritionists on my team, has also experimented with IF. She found it difficult to do a strict fast, where you would only have water, and instead will have coffee with MCT oil and collagen in the morning. She found that because of her history with digestive issues, waiting before eating in the morning has actually helped her feel less bloated and have more energy. She did add that if she’s hungry or feels like she can’t maintain the fast she doesn’t hesitate to eat. This highlights that you can find a way to incorporate some of the principles of IF in a way that works for you.
In my opinion, the people who would benefit from IF the most are those who already have a good relationship with food and eat a well-balanced diet, but are looking for other ways to optimize their health. Because there are no dietary guidelines, it’s possible for someone to do IF but still eat a diet full of processed foods. You may lose weight because your eating window is shorter but you wouldn’t be doing much for your health overall and you might be at greater risk of nutrient deficiencies and slowing down your metabolism.
The main takeaway from the research backing IF is that North Americans in general consume way too much food and many of our modern diseases stem from overeating and not moving enough. Most people would benefit from eating in moderation, letting your body burn fat between meals and only eating when hungry or when you know you tend to get hungry, and limiting nighttime eating.
Alirezaei, M., Kemball, C. C., Flynn, C. T., Wood, M. R., Whitton, J. L., & Kiosses, W. B. (2010). Short-term fasting induces profound neuronal autophagy. Autophagy, 6(6), 702-10. doi: 10.4161/auto.6.6.12376
Antoni, R. Johnston, K.L., Collins, A.L., & Robertson, M. D. (2014). The Effects of Intermittent Energy Restriction on Indices of Cardiometabolic Health. Research in Endocrinology, 2014(2014). doi: 10.5171/2014.459119
Barnosky, A.R., (2014). Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings. The Journal of Laboratory and Clinical Medicine, 164(4), 302 - 311. doi: 10.1016/j.trsl.2014.05.013
Leonie K. H., Steven R.S., Corby K. M., Stephen D. A., & Ravussin, E. (2005). Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism. The American Journal of Clinical Nutrition, 81(1), 69–73. doi: 10.1093/ajcn/81.1.69
Longo, V. D., & Mattson, M. P. (2014). Fasting: molecular mechanisms and clinical applications. Cell metabolism, 19(2), 181-92. doi: 10.1016/j.cmet.2013.12.008