Fasting has been used for thousands of years to keep us well, and it’s the most profoundly effective metabolic intervention I know of. Not only does it upregulate autophagy and mitophagy — natural cleansing processes necessary for optimal cellular renewal and function — but it also triggers the generation of stem cells. The cyclical abstinence from food followed by refeeding also massively stimulates mitochondrial biosynthesis.

There’s even evidence to suggest fasting can help prevent or even reverse dementia, as it helps your body clean out toxic debris. By lowering insulin, you also increase other important hormones, including growth hormone (known as “the fitness hormone”), which is important for muscle development and general vitality.

Most of these rejuvenating and regenerating benefits occur during the refeeding phase, not the “starvation” phase. The same holds true for nutritional ketosis, which produces the greatest benefits when pulsed. I’ve written a number of articles on both of these topics. Here, the focus is on why these two strategies work best when combined.

Fasting Is a Powerful Tool for Rejuvenation and General Health

Research shows fasting is a powerful lifestyle tool for combating obesity, insulin resistance and related health problems, including cancer. The reason for this is because when autophagy increases, your body starts breaking down and recycling old protein, including beta amyloid protein in your brain believed to contribute to Alzheimer’s. Then, during the refeeding phase, growth hormone increases, boosting the rebuilding of new proteins and cells. In other words, it reactivates and speeds up your body’s natural renewal cycle.

While water-only fasting can be extremely beneficial for those struggling with excess weight and/or Type 2 diabetes, compliance can be difficult. Fortunately, research has confirmed that similar results (albeit not as profound) can be achieved through intermittent fasting, i.e., following a meal-timing schedule where you’re fasting for at least 16 hours every day and eating all of your meals within eight consecutive hours.

There are also other intermittent fasting plans where you dramatically cut back on your calories for a certain number of days each week, while eating normally during the remainder. The 5-to-2 intermittent fasting plan is one such example. The fasting mimicking diet, developed to match the effects of water-only fasting, is another. Most if not all of these plans have similar benefits, which include:^1,2,3,4

Upregulating autophagy and mitophagy	Increasing growth hormone by as much as 1,300 percent in women and 2,000 percent in men,5thereby promoting muscle development and vitality
Shifting stem cells from a dormant state to a state of self-renewal	Preventing, slowing the progression of, and reversing Type 2 diabetes
Boosting mitochondrial energy efficiency and biosynthesis	Reproducing some of the cardiovascular benefits associated with exercise
Lowering inflammation	Improving pancreatic function
Improving circulating glucose and lipid levels	Protecting against cardiovascular disease
Reducing blood pressure	Modulating levels of dangerous visceral fat
Improving metabolic efficiency and body composition	Reducing low-density lipoprotein and total cholesterol
Significantly reducing body weight in obese individuals	Improving immune function6
Boosting production of brain-derived neurotrophic factor, which stimulates creation of new brain cells and triggers brain chemicals that protect against brain changes associated with Alzheimer’s and Parkinson’s disease7

New Research Questions Effectiveness of Intermittent Fasting When Still Eating Poorly

While intermittent fasting may sound like a panacea against ill health and excess weight, it alone may not provide you with all of these benefits. The quality of your diet plays an important role if you’re looking for more than mere weight loss. More specifically, recent research highlights the importance of nutritional ketosis when intermittently fasting.

The study^8,9 in question examined the effects of intermittent fasting on weight loss and metabolic disease risk parameters in 23 obese volunteers. The study lasted for three months. Between 10 a.m. and 6 p.m., the participants were allowed to eat whatever they wanted in any quantity. For the remaining 16 hours, they were only permitted water or calorie-free drinks. The outcomes were then compared to a nonintervention control group from a previous fasting trial.

Overall, participants consumed about 350 fewer calories per day and lost just under 3 percent of their body weight. Systolic blood pressure also dropped about 7 mmHg, compared to the historical control group. Lead author Krista Varady, associate professor at the University of Illinois at Chicago, commented on the results saying,¹⁰ “The take-home message from this study is that there are options for weight loss that do not include calorie counting or eliminating certain foods.”

While these findings are similar to other intermittent fasting studies, the participants’ weight loss was slightly less than what’s been observed in other studies. Trials of alternate-day fasting and the 5-to-2 fasting plan have found people lose between 3 and 8 percent in eight to 52 weeks. According to the authors, “We speculate that this difference in weight loss is due to greater overall caloric restriction achieved with other forms of intermittent fasting …”

While this may sound “good enough,” there’s an important detail that needs to be addressed. While participants did lose weight, other metabolic health parameters did not significantly improve compared to no-treatment controls, including visceral fat mass, diastolic blood pressure, LDL cholesterol, HDL cholesterol, triglycerides, fasting glucose and fasting insulin.