You’ve likely encountered a patient, friend, or family member who has expressed interest in fasting. Intermittent and periodic fasting have received plenty of press coverage in recent years for their purported health benefits, including weight loss, exercise endurance, immune function, and more.
Intermittent fasting (IF) refers to fasts lasting from 12 to 48 hours that are repeated every 1 to 7 days, whereas periodic fasting (PF) lasts between 2 and 7 days and is repeated at least once per month. Furthermore, there are two types of PF. The first is water-only and the second is a fast-mimicking diet (FMD), which refers to consuming only a plant-based, calorie-restricted diet that consists of low proteins, low sugars, and high unsaturated fats. This combination recapitulates the effects of a water-only fast on IGF-1, IGF binding protein 1 (IGFBP-1), ketone bodies, and glucose.
An emerging corpus of research has focused on the potential of fasting to prevent and treat chronic disease, as well as boost longevity. Let’s take a closer look.
According to an article published in Nature Aging, IF and PF/FMD trigger pathways that activate alternative metabolic modes that focus on “conserving energy and on protecting the organism while enduring extended periods of food deprivation to optimize survival and reproduction once food becomes available.” Intriguingly, the refeeding period plays an equally important part in regeneration, as well as rejuvenation of organs, cells, and organelles.
“In humans, the alternation of fasting and refeeding periods is accompanied by positive effects on risk factors for aging, diabetes, autoimmunity, cardiovascular disease, neurodegeneration and cancer,” the authors wrote. “But not all fasting interventions are equal, and some are associated with smaller beneficial effects as well as side effects, including, in some cases, reduced longevity.”
Health effects of intermittent fasting
The Nature Aging authors cited studies that showed IF resulted in weight loss, as well as positive effects on metabolic markers and decreased insulin resistance. IF was correlated with decreased levels of low-density lipoprotein (LDL); the metabolic regulator triiodothyronine; and soluble intracellular adhesion molecule-1 (sICAM-1), an age-associated inflammatory marker.
Other studies demonstrated that IF led to a reduction in weight gain, better sleep, decreased deterioration in cardiac performance caused by age and diet, decreased oxidative stress, and better blood pressure levels.
Along the same lines, in a review published in Clinical Diabetes and Endocrinology, the authors found evidence that IF helps improve diabetes and decreases body weight; lowers fasting glucose, fasting insulin, levels of leptin, insulin resistance; and increases adiponectin levels.
Because IF is effective at attenuating the harms of type 2 diabetes, it makes sense that it could be a useful dietary intervention. Although the authors recommend this therapy, they urge caution.
“Patients taking insulin or sulfonylurea medications should be closely monitored by their healthcare provider in order to prevent hypoglycemic events,” they wrote. “Because studies are demonstrating a decreased need for insulin in patients who follow intermittent fasting protocols, blood glucose levels and medication titration should be observed closely by the physician. Physicians should help patients make appropriate adjustments to their medications, especially on days of fasting.”
They added, “Physicians may choose to have patients keep daily blood sugar and weight logs and send them weekly or biweekly via electronic message in order to assist providers in medication titration over time. Of note, while the goal of adapting this pattern of eating is to reduce or eliminate the need for medications, including insulin, there are situations in which insulin may be necessary, such as severe hyperglycemia. Failure to do so may result in significant consequences, such as the development of hyperosmolar hyperglycemic syndrome.”
To learn more about the effects of intermittent fasting on diabetes, click here.
Health effects of periodic fasting
Similar to IF, the authors of the review published in Nature Aging cited research that showed PF—in particular, its subset form, FMD—decreased weight, blood pressure, and abdominal circumference. They also noted that FMD reduced risk factors for heart disease, diabetes, and cancer by lowering blood pressure and BMI, as well as levels of IGF-1, glucose, triglycerides, cholesterol, and C-reactive protein. Importantly, these changes were sustained for months following a return to normal diet.
The role of ketogenesis
According to the NIH, weight loss may not be the key impetus behind the health and mortality benefits observed during IF. Instead, these benefits may arise from ketogenesis, when the body switches its fuel from glucose to ketones. Ketones signal effects on cell and organ functions.
Increased serum levels of ketones boost the body’s defense vs oxidative and metabolic stress and trigger the repair and removal of damaged molecules. These effects endure into the non-fasting period and enhance glucose regulation, boost resistance to stress, and stymie inflammation, thus resulting in lasting adaptive responses. In the aggregate, these broad benefits help battle disease and boost mental and physical performance.
Research indicates that fasting can help fight disease and prolong life. Nevertheless, in the United States and other developed nations, there’s a propensity to eat three square meals a day plus snacks, which may make it challenging for some people to adapt to this pattern of eating. Moreover, this pattern of eating can lead to certain complications in patients with chronic disease such as diabetes.
For any physician considering fasting for their patients, it may be a good idea to further research the intervention, consult with a dietitian or nutritionist, and have patients phase in fasting gradually.
Click here to read Here's how intermittent fasting can be safe and effective on MDLinx.