Fasting: Why These Diets Are Getting So Much Attention?

by Amy Hendel, P.A. Health Writer

Fasting diets are seen by many people as a surefire way to lose weight and improve one's health, and as a means of preventing or treating numerous health conditions. But is fasting really the miracle therapy so many proponents claim it to be?

Breast cancer and fastingBreast cancer is the number one cause of death among women in developing countries and it’s the second most common cause of death in developed countries. Many studies have examined diet, in particular, when evaluating programs that can limit breast cancer risk or prevent recurrence. Results of those studies have been mixed, at best. A study published in JAMA Oncology in August 2016 looked at how the timing of meals can have an impact on metabolic health and cancer, especially the recurrence of breast cancers.

The study examined the potential benefits of an overnight fast. More than 2,400 women — all with early stage breast cancer — participated in the Women’s Healthy Eating and Living study (1995-2007), fasting nightly. Women who fasted for less than 13 hours had a 36 percent higher risk of breast cancer recurrence compared to women who fasted overnight for 13 or more hours. Nightly fasting also seemed to improve glycemic control and supported deeper, longer sleep. The researchers concluded that their findings could support a novel, no-cost way to lower the risk of breast cancer recurrence.

Fasting impact on cancer, diabetes, heart disease, and other conditions

A 2015 study in mice, published in the journal Cell Metabolism, found that following a calorie-restricted diet that mimics fasting for five days a month for three months may promote a longer life and also reduce the risk factors for a number of conditions, including certain cancers, diabetes, and heart disease. As mentioned above, fasting seems to modulate blood sugar levels and also appears to limit general inflammation in the body. Persistent levels of inflammation are associated with an elevated risk of chronic conditions. The concept of periodic fasting also seems to reboot the immune system, literally clearing out damaged cells and helping to regenerate news ones.

Some children with epilepsy seem to respond to a fasting diet, according to Reshmi Srinath, M.D., in a New York Daily News article published October 10, 2016. “But some doctors are skeptical about the overall efficacy of fasting diets,” Dr. Srinath writes.

Fasting and Alzheimer’s disease

Fasting much of the day and then eating within a specific time window has been a research and personal program that Mark P. Mattson, Ph.D., follows. In an article in the Johns Hopkins Health Review, Dr. Mattson, a professor of neuroscience in the Johns Hopkins School of Medicine, has conducted research suggesting that fasting for several days a week might provide a multitude of positive benefits: it could possibly improve mood and memory while protecting against neurodegenerative diseases such as Alzheimer's and Parkinson’s. The theory is that this and other approaches to fasting help improve neural connections in a part of the brain called the hippocampus, while protecting against accumulations of amyloid plaque implicated in the genesis of Alzheimer’s disease. “Fasting is a challenge to your brain,” Dr. Mattson says in the article.

Understanding the impact of fasting

Why does fasting seem to nudge certain physiologic changes that dieting does not? Whenever you eat, you store glucose in your liver in the form of glycogen. It takes about 10 to 12 hours to fully deplete your glycogen stores. (They also deplete faster with vigorous exercise.) Once you use up glycogen, the body burns fat stores, turning them into ketone bodies for energy. Ketones promote positive changes in your brain, which helps to promote better learning, memory, and overall brain health. If you’re eating all day long, or even consuming three meals plus snacks during your waking hours, your body never has a chance to fully deplete glycogen stores.

When I interviewed Andrea N. Giancoli, MPH, a registered dietitian and nutrition communications consultant, by email on the subject of fasting, she noted that "there isn’t enough good research/scientific evidence to support recommending fasting as an effective weight loss technique that can be sustained healthfully long term or as a lifestyle."

She added that some of the fasting studies had very small numbers of subjects and needed to be replicated with many more participants.

I asked Ms. Giancoli to review a small study involving 30 subjects, using an “alternate day fasting” program. Subjects were provided with all meals and monitored for eight weeks, with one group following the alternate day fasting diet while the other group followed a calorie-restricted diet. Subjects continued the diets for an additional 24 weeks on their own. Both groups had weight loss (the fasting group lost about 2.4 extra pounds) and positive changes in their cholesterol profiles, but the fasting group had dramatic changes in their triglyceride levels.

Ms. Giancoli pointed to the small number of participants, the small differential in weight loss between the two groups (maybe the fasting group actually under-reported calories consumed on fasting days), and the fact that “we don’t know how each group did after a year or two years. Ultimately, is this [fasting] sustainable?”

She also wondered if fasting could really be tested in a way that would apply to real life —because life is unpredictable and temptation is always an issue.

**Next: Fasting Part 2: Types of Fasting Diets

Amy Hendel, also known as The HealthGal, is a Physician Assistant, nutritionist and fitness expert.As a health media personality, she's been reporting and blogging on lifestyle issues and health news for over 20 years. Author of The 4 Habits of Healthy Families, her website offers daily health reports, links to her blogs, and a library of lifestyle video segments.

Amy Hendel, P.A.
Meet Our Writer
Amy Hendel, P.A.

Known as "The HealthGal", Amy Hendel P.A. is a medical and lifestyle reporter, nutrition and fitness expert, health coach and brand ambassador. Trained as a physician assistant, she maintains a health coach private practice in New York and Los Angeles. Author of The Four Habits of Healthy Families, find her on Twitter @Healthgal1103 and on Facebook @TheHealthGal. Check “Daily Health News” at Her personal mantra? “Fix it first with food, fitness, and lifestyle.”