Intermittent Fasting: What You Need to Know
Intermittent fasting (IF) has become increasingly popular over the last year – there are countless books, Facebook groups, and Reddit discussions by those who swear by the lifestyle. Those who love it argue that it is different than a diet because intermittent fasting does not dictate what you can and cannot eat, but instead when you eat.
Interestingly, intermittent fasting is one nutrition trend that does have some science to back it up. Promising research outcomes are well documented, including positive changes in insulin resistance, cholesterol, aging and gene expression, mental clarity, and weight loss. And fasting isn’t exactly a new idea. People have been fasting for religious and health reasons for hundreds of years. But before jumping on the fasting bandwagon, make sure you understand the background, who may benefit from intermittent fasting, and who should probably skip it.
What is intermittent fasting?
Intermittent fasting refers to an eating pattern with a set window of eating and fasting. There are several types of patterns, including the 16:8 method, alternate-day fasting or eat-stop-eat, 20:4, OMAD, or one meal a day. When following the 16:8 method, you fast for sixteen hours while keeping all meals in an eight-hour window. This method is the most popular because, for many people, it (nearly) matches a typical pattern of eating. For example, if you finish eating by 7 pm, then you don’t eat again until 11 am.
We know that avoiding food a few hours before we go to sleep at night is incredibly important. Studies have shown that those who eat later tend to weigh more as compared to those who stop eating earlier in the evening, even if they take in the same amount of calories. If we are following circadian rhythms and giving our body a chance to rest at night, then we naturally fast overnight, allowing our body to heal and digest. This time is a restorative period for our body. The question is whether extending this fast increases those therapeutic benefits.
What is a “dirty” versus “clean” fast?
Enter any online group dedicated to fasting and you will see this debate pop up. Those who “dirty fast” will argue that anything less than 100 calories will not affect their fast. Those who “dirty fast” will often do so to have a little cream in their coffee. Some experts argue that if weight loss is the goal then drinking a little cream in the coffee won’t break the fast enough to change results and that it may help with adherence to the pattern. The majority, however, will argue that fasting is fasting, that anytime you eat or drink something, your body will respond, 100 calories or not. True “clean fasting” means sticking to water, coffee, and herbal teas.
What are the potential benefits of intermittent fasting?
Dietitians, doctors, and mothers everywhere have always argued that breakfast is the most important meal of the day, so how can this type of fasting be beneficial? Before diving into the science, on a surface level, a person is less likely to overeat if they stop eating at a specific time. Those who follow 16:8 correctly will likely eat less and prevent the mindless snacking at night that happens to so many people. By creating a hard stop for eating, there will be a natural reduction in overall caloric intake as well as decrease for the opportunity to eat processed snacky foods late at night.
But on a deeper level, there are metabolic benefits that are also very promising. While much of the research initially examined the effect of fasting on rats, some small studies in humans also exist.
Weight loss. Aside from caloric restriction, if we aren’t eating, then our pancreas isn’t releasing insulin. Insulin is released in response to increases in our blood sugar after our food is digested, specifically after eating carbohydrates. Insulin helps to shuttle glucose into our cells to be used as energy or stored. If this process doesn’t happen, then our stored energy can be released - ideally from fat cells. Fasting also stimulates the release of human growth hormone – a hormone that also encourages the body to burn fat as fuel.
Metabolic improvements. As above, if your body is in a fasted state, then you won’t be releasing insulin. Aside from the weight loss benefits, this can lead to a reduced risk of developing Type 2 Diabetes. Several studies in both humans and rats have demonstrated reductions in blood sugar and fasting insulin through intermittent fasting. Noted metabolic improvements also include positive changes in cholesterol and lipids levels.
Cellular repair and autophagy. As when we sleep at night, when the body is in a fasted state, it has a chance to rest and repair. This reparative window may be magnified with an extended fast. Cellular autophagy essentially means the body is ridding itself of cellular waste and debris.
Improved brain function. Intermittent fasting has been shown to reduce oxidative stress and decrease overall inflammation in the body. Further, intermittent fasting can also increase an essential hormone for the brain, brain-derived neurotrophic factor (or BDNF). Anecdotally some will also report feeling more clear-headed while fasting.
What are the downfalls, and who should avoid intermittent fasting?
While some will certainly see benefit using intermittent fasting, like any other diet or meal plan, the results are highly individual. For some people there are significant downfalls and important tips to consider.
Eat nutrient-dense food. If you enter into your eating window starving and reach for quick, sugary processed foods, the whole premise of fasting backfires. Planning meals and knowing what you will eat is key to success. The food you break your fast with should be nutrient-dense, high in protein and healthy fats. Additionally, the smaller the eating window, the less of a chance you have to ensure your body is getting the nutrients it needs. I rarely suggest anything less than a 16:8 pattern because of this very reason.
Energy/adrenal dysfunction. If you are someone suffering from low energy despite eating well or have been told you have HPA axis dysregulation (often incorrectly called “adrenal fatigue”), then fasting is not a good idea for you. It can lead to additional stress on your already stressed body. Eating regularly, nourishing nutrient-dense foods to support consistent energy levels is more important.
Hormonal shifts. While some women do just fine with intermittent fasting, others may not benefit. Our hormones closely link with our blood sugar balance. If you are trying to get pregnant or have other hormonal imbalances, it is not a good time to start fasting. In one of the studies I mentioned above with regards to blood sugar, while men saw a benefit, women had worse outcomes with blood sugar control. While a small study, it is important to note that due to our beautifully complex wiring, women may respond differently than men.
Eating disorders or orthorexic tendencies. If you have ever had an eating disorder or find yourself becoming obsessive about food restriction or binging, then intermittent fasting is not a great idea. The rules of when to eat can be triggering, or waiting to eat too long can lead to binging. Some may feel shame or that they have failed if they aren’t able to stick to the self-prescribed window of eating. None of these scenarios are supportive for your health.
Medications. If you are taking prescription medications that require food or need to be taken at specific times in the day, then you absolutely should not skip or wait for your window. If you are taking medications for blood sugar, you also can inadvertently lower your blood sugar to an unsafe level. A conversation with your physician or healthcare practitioner is essential before starting any fasting method.
Is Intermittent Fasting a Long Term Solution?
It’s hard to say whether intermittent fasting will fade behind the next shiny diet trend. While not always my first choice of strategies, it can be a starting point for some people who need a bit of structure without a specific diet. If you do decide to try it, you may consider starting with a few days a week and see how you feel. Listen to your body – if something doesn’t feel right (light-headed, more fatigue, overeating in your window, obsessing over food windows), there are many other ways to support and nourish your body.