What is the history of fasting?
Fasting has been practiced for centuries mainly pertaining to religious beliefs. It became popular as a weight loss diet in 2012 when the book the “The FASTDIET” was published. Fasting has been gaining popularity again recently as a way to lose weight. There are many different fasting routines. Many people will eat during 8 hours of the day and fast the remaining 16. Another option is to limit calorie intake to less than 500 calories per day for two days per week.
Can you lose weight with an intermittent fasting diet?
Intermittent fasting has been shown to promote weight loss. The idea is that less calories are consumed overall which leads to weight loss. Different types of fasting diets show different weight loss results. Some people like intermittent fasting because it does not require calorie counting, label reading, measuring portions, etc. A study published in 2018 showed that the participants who followed the 5:2 diet version for twelve weeks lost 7.1% of their weight. Other studies show that fasting diets have no advantage over daily calorie restricted diets. People often lose the same amount of weight when comparing fasting diets with calorie restricted diets. For some fasting is not a sustainable diet. Many people have a difficult time complying with the fasting diet regimens.
What about fasting for other health reasons?
Diabetes
Since the overall concept of fasting is to reduce calorie intake, it improves insulin resistance. Fasting for a period of time leads to increased sensitivity to insulin and lowers insulin levels in the body. This leads to overall improvement in blood sugar control. If someone is restricted to only eating certain hours of the day then their blood sugars should be lower overall but they are also at risk for low blood sugars. It is important to talk with your health providers about starting an intermittent fasting diet.
Heart Disease
Intermittent Fasting may also improve cholesterol. This happens due to the overall decrease in calorie intake which results in weight loss. Weight loss reduces total fat mass and can lead to lower total cholesterol, lower density cholesterol (LDL) and triglycerides. Fasting is not more beneficial than a low fat, Mediterranean or anti-inflammatory diet for management of heart disease. It is also not typically sustainable for heart health.
Cancer
Even though there is very little evidence, people choose to fast during cancer treatment. It has been proposed that fasting reduces the side effects of treatment as well as making cancer cells more susceptible to treatment. In addition, the reduction in calories and carbohydrates can reduce insulin levels in the body. This is especially important to cancer survivors since insulin is a growth hormone. Overall it is not recommended to fast to prevent or treat cancer. This can lead to further unwanted weight loss and malnutrition. Fasting can also inhibit a healthy immune system. It is essential to talk with your health care providers about fasting to make sure you are getting in adequate nutrients to keep your body healthy.
What are the risks of intermittent fasting?
Intermittent fasting does not come without some risks. It is essential to communicate with your physician if you have diabetes. It may be pertinent to change your diabetic medications during fasting periods to prevent blood sugar lows or hypoglycemia.
If you are a cancer survivor or undergoing treatment for cancer, it is not recommended to fast. It is important to get all the nutrients you need to keep your body healthy. Practicing intermittent fasting long term also increases risk of malnutrition as well as vitamin and mineral deficiencies.
This is not is not an appropriate diet if you have a history of an eating disorder or disordered eating patterns. Some people may experience fatigue while fasting. This could affect your daily activities including work productivity, driving or caring for children.
Note from the Dietitian
As a dietitian I do not recommend intermittent fasting but I am aware one size does not fit all for health and wellness goals. Intermittent fasting may make sense to some people if time structure appeals to them as well as the idea that they are reducing their calorie intake without “dieting”. There are no specific recommendations or guidelines for intermittent fasting, so I highly recommend you communicate with your health providers. It is a good idea to meet with a dietitian to make sure you are taking in the essential nutrition and that the foods consumed during eating windows are very high quality.