If you’ve ever subscribed to an exciting ‘latest and greatest’ diet, you have plenty of company. It seems as if every day a new diet trend emerges, making promises that seem too good to be true. However, the challenge of decoding the secret to successful weight loss is often clouded in mystery and anecdotal evidence. Of the handful of diet options that buck this trend, one that is quickly regaining renewed interest and acceptance is fasting.


The concept of fasting is hardly new

Dating back thousands of years, its health benefits were thought to extend far beyond mere weight loss. Plato, Hippocrates, and Aristotle were firm believers in the healing powers of the technique, viewing it as an antidote to all kinds of sicknesses. Paracelsus, considered a father of western medicine, declared fasting “the greatest remedy, the physician within.”

The practice of fasting essentially mimics the eating patterns of our ancestors who lacked readily available access to food sources. As hunter-gatherers, humans, like most mammals, would cycle between periods of fasting and feasting. The human body has evolved in response to this cycle of nourishment by switching between two accessible sources of energy—carbohydrates stored in liver and muscle in the form of glycogen for immediate energy needs and fat stores that supply longer energy requirements during extended periods without food. While most of the modern world has since adopted a standard diet consisting of three meals per day, the body continues to fast—for about eight hours every night.

Many questions have surrounded the practice of fasting and its perceived benefits. Can fasting really lead to meaningful weight loss? Can it help support healthy aging and have beneficial effects on cholesterol levels, inflammation, and glucose sensitivity?


Science has caught up with this age-old practice

It is a well-known fact that fasting for more than 1-2 days has been shown to initiate ketosis. This normal metabolic process allows the body to continue functioning after running out of carbohydrates by switching to burning fat for energy producing ketones. Recently, it has been shown that breaking down fat for energy can also release persistent organic pollutants (POP) that become sequestered in adipose tissue. POPs, such as certain organochlorine pesticides and numerous industrial chemicals, are highly attracted to lipids. Their accumulation in adipose tissue has been associated with numerous disorders including lipotoxicity and cardiovascular disease.

Beyond fat burning, fasting also acts to lower insulin and insulin-like growth factor (IGF-1). Blunting of the growth hormone receptor/IGF-1 pathway has been thought to switch the body from growth mode to repair mode, slowing down the aging process and switching on numerous DNA repair genes. These fasting-induced cellular processes have also been associated with immune system renewal. Fasting can promote stem cell-based regeneration through recycling of older, damaged white blood cells followed by the formation of new cells once normal feeding is resumed. Studies have shown that these fasting-induced processes extended longevity in numerous species, including bacteria, worms, and rodents. In humans, fasting has similarly been shown to protect against age-related diseases including hypertension, cancer, dementia, cardiovascular disease, and diabetes.

Unfortunately, the benefits of calorie restriction are enjoyed by few because of the simple fact that it is hard to just say no to food. For one, fasting can be highly inconvenient. Foregoing food can disrupt daily activities through diminished energy levels and hunger pains, making it impractical for most individuals. Additionally, when taken to extremes, prolonged fasting can be associated with adverse health events, particularly in the elderly and people with low body fat or diabetes.


The evolution: The ‘fasting with food’ discovery

More recently scientists at the Longevity Institute of the University of Southern California lead by Professor Valter Longo have developed a diet that safely mimics fasting for five days per month using actual food. Appropriately named the Fasting Mimicking Diet, or FMD, this meal program replicates the beneficial effects of a prolonged fast while nourishing the body with essential micronutrients.

In a recent study funded by the National Institute on Aging, subjects on FMD demonstrated reduced risk factors for a range of issues including cancer, diabetes, cardiovascular disease, and aging. Dieters in the study completed 3 FMD cycles and were allowed to eat as they normally would for 25 days of the month. During the other five days, participants would consume a ketogenic diet high in micronutrients: 1,090 calories on day one and 725 calories from days 2-5 consumed from food options such as vegetable soup, kale crackers, and chamomile tea. Participants in the study experienced a 3% reduction in body weight that lasted through the end of the 3-month study. Coupled with the high compliance rates and safety scores, the initial findings of this study indicate that FMDs may be a promising option for promoting healthy lifestyles.

FMDs seemingly offer a reboot of an age-old technique that offers the potential to normalize fasting by reducing the psychological burden and physical demand while providing its many health benefits.

Whatever fasting diet you choose, challenges are bound to crop up, but in a world that says “we can’t have our cake and eat it too,” science is helping us get there.

Kurt Hong, MD, PhD, FACN
Dr. Kurt Hong is the Executive Director of the Center for Clinical Nutrition & Applied Health Research, and Associate Professor of Medicine, University of Southern California. Dr. Hong earned his Doctor of Medicine from Harvard Medical School and his Doctor of Philosophy, Cellular and Molecular Pathology from UCLA. Dr. Hong has been involved in obesity and metabolic disease research over the past 15 years. His research interests include the study of macro and micronutrients affecting energy metabolism, weight status and related complications, including metabolic syndrome. Dr. Hong is an investigator on NIH-funded studies and has served on multiple editorial boards and national organization committees - including the Obesity Society, Southern California Clinical, and Translational Science Institute, and the American Society for Nutrition. He is dual board-certified in internal medicine and clinical nutrition. As a well-recognized expert in his field, Dr. Hong contributes regularly to national magazines and other media outlets and has been voted three times by his peers to Best Doctors in AmericaTM. Dr. Hong is also on the Scientific Board at L-Nutra, the leading nutritechnology company focused on the science and benefits behind fasting, and developer of ProLon®.


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