Intermittent Fasting: The Research

Have you heard about intermittent fasting? Abbreviated IF, intermittent fasting is a popular diet at the moment and I have been getting so many questions about it. If I’m being honest, during my undergraduate study of nutrition – the topic was never brought up. We were taught about the benefits of eating every 3-5 hours with a mix of macro-nutrients to stimulate metabolism and regulate blood glucose levels. When people started to ask about IF, I became curious myself, so I decided to do some research.

What is Intermittent Fasting?

IF involves avoiding intake of all or most food for an extended period of time, followed by a “feeding” period where food is eaten as desired.

Different Forms of IF

(Descriptions provided by Dr. Vincent M. Pedre, a gut health specialist that “suggests intermittent fasting to many of his patients”) (1)

1. 12 hour fast, usually most of which are spent sleeping.
2. 8 hour window: creates 16-hour daily fasting period.
3. Alternate-day fasting: consists of “feed day” where individuals eat whatever they want and a “fast day” where individuals consume only 25% of their normal intake.
4. The 5:2 plan: individuals eat normally five days every week and eat only 500-600 calories on the other two days, focusing on protein, healthy fats and vegetables.

Disclosure:

I do have to disclose that I have a bias in writing this post. Last year, I was able to complete a rotation of my dietetic internship at an eating disorder clinic. I learned so much about diet culture, susceptibility and development of eating disorders, the neurobiology behind disordered eating, the impact of disordered eating on mental health and vice versa. After being exposed to this population, I would never recommend such an intense, restrictive diet to anyone. Knowing how harmful the diet mentality and intense calorie restriction can be, I don’t view the diet as safe in terms of physical or mental health. I am much more comfortable recommending a regular, balanced diet to all populations. I came across a blog post by an Eating Disorder Dietitian that emphasizes the negative findings of each study and lack of applicability to women. It is really well done and you can find it here. I decided to look at the research with my own fresh eyes, and here’s what I found…

Proposed Benefits:

There are many proposed benefits to intermittent fasting. Each study that I reviewed showed significant results for weight loss, improved insulin sensitivity (resulting in more regulated blood glucose levels after consuming carbohydrates), and decreased risk of cardiovascular disease through improved cholesterol and blood pressure levels. Some studies also showed improved cognitive performance through increased production of neurons that have protective effects against neurodegenerative diseases (Alzheimer’s, Parkinson’s, Huntington’s Diseases) and traumatic injury, and increased production of ketones leading to resistance to seizures. (3) (4). Because of these claims and more, many studies suggest that IF has potential to lengthen life span.

The Caveat:

Most of this research is limited to animals (rats). The majority of human studies only evaluate weight loss, not long term effects, or focus on specific groups of people like those with diabetes or rheumatoid arthritis.

Fasting and Cancer

One article I read made this claim: “Fasting can have positive effects in cancer prevention and treatment.” (4). It proceeded to detail that there was decreased incidence of lymphomas and tumorigenesis in mice that were forced to fast. There is no doubt that people only read this far and this may lead to headlines like,  “IF CAN PREVENT CANCER” because of these findings. HOWEVER, the paragraph then states: “However, the major decrease in glucose, insulin and IGF-1 caused by fasting, which is accompanied by cell death and/or atrophy in a wide range of tissues and organs including the liver and kidneys, is followed by a period of abnormally high cellular proliferation in these tissues driven in part by the replenishment of growth factors during refeeding. When combined with carcinogens during refeeding, this increased proliferative activity can actually increase carcinogenesis and/or pre-cancerous lesions in tissues including liver and colon.” So while IF has been shown to have preventative effects for cancer, it also has been shown to increase cancer risk. Take this as you will.

Fasting for Rheumatoid Arthritis and Asthma

I also read about four studies that showed promising results for patients with RA. When RA patients fasted and then resumed a normally-timed, vegetarian diet – pain and inflammation were very much reduced (4). Therefore, if you are someone that struggles with RA, this may be something worth talking to your doctor about.

For patients with asthma, fasting reduced oxidative stress (4). However, patients must be willing to make long-term changes to their diet because the inflammation returned with normally-timed meals.

Blood Pressure

Blood pressure was reduced by a mean of 20 mm Hg in patients with borderline hypertension. However, these people fasted for 13 days – without food and only water. When resuming normal diet, the blood pressure only remained significantly lower for an average of 6 days (4).

My Interpretation:

I have heard a few convincing testimonials from people that have done the intermittent fasting diet. People lose weight and claim to “feel amazing.” I’m not surprised by the weight loss. By limiting intake of nutrients for extended periods of time, there is no doubt in my mind that a person would be eating significantly less. As we know, weight loss occurs when we are in a caloric deficit (eating less calories than we are burning off). But is intermittent fasting necessary for weight loss? Absolutely not. There are other less rash ways to increase calories burned or decrease calories consumed that do not include going longer than 12 hours without eating anything.

One study that I read about (4) detailed the beneficial effects of our bodies’ “hunger response”: including cardiovascular effects, tumor suppression, immune function, improved cognition, improved stress tolerance. I don’t know about you, but I’ve never heard that I had to be “hungry” to be “healthy.” People have been eating regularly for decades, and there are several other routes for these benefits (i.e. eating fruits, vegetables, fiber and phytonutrients, as well as living a physically and mentally healthy, balanced life) that sound much more appealing to me.

I do think that IF has shown significant results and may be promising for specific populations. However, I think there is MUCH more research to be done in order to evaluate efficacy in humans and long term effects on overall health.

1. Pedre, Vincent. The Different Types of Intermittent Fasting + Which One is Right for You. Mind Body Green. May 17, 2017.
2. Horne, Benjamin D., Muhlestein, Joseph, Anderson, Jeffrey. Health effects of intermittent fasting: hormesis or harm? A systematic review. The American Journal of Clinical Nutrition, Volume 102, Issue 2, 1 August 2015, Pages 464-470.
3. Anson et al. Intermittent fasting dissociates beneficial effects of dietary restriction on glucose metabolism and neuronal resistance to injury from calorie intake. Proceedings of the National Academy of Sciences of the United States of America. Volume 100, Issue 10, May 13, 2003, Pages 6216-6220.
4.  Longo, Valter, Mattson, Mark. Fasting: Molecular Mechanisms and Clinical Applications. Cell Metabolism. Feb 4, 2014; Volume 19, Issue 2, pages 181-192.