Find out what a Carilion Clinic dietitian says about the risks and benefits, as well as how to get started.
Fasting is a time-honored spiritual practice in many cultures, one which could prove to offer physical benefits as well.
There is currently considerable public and scientific interest in determining whether intermittent fasting—or intentional periods of dietary restriction—may offer a potentially effective approach for weight management and improving health.
We spoke with registered dietitian Angela Charlton, who works with our Community Health and Outreach team at Carilion's Morningside Urban Farm. The following is Angela's read on research in the Annual Review of Nutrition (pdf) on the types of intermittent fasting, how it works and how to approach it safely.
Types of Intermittent Fasting
The paper included an overview of the topic and summarized the existing research, which categorizes the various regimens as:
Complete Alternate-Day Fasting
This regimen alternates days of regular intake with days of eating no energy-containing foods or beverages.
Modified Fasting
With this regimen, people spend several days consuming only 20 to 25 percent of their energy needs, then alternate with regular intake during non-fasting days.
Time-Restricted Feeding
This regimen limits consumption to a specific timeframe every day.
Religious Fasting
Regimens that people undertake for religious or spiritual purposes span a variety of regimens.
How Fasting Works
Though human studies were limited, the review offered encouragement and recommendations for further research. The findings provided some support to theories that intermittent fasting regimens might:
- Improve metabolism
- Result in weight loss
- Reduce risks of obesity and related conditions
- Reduce risks of chronic diseases such as diabetes and cancer
The authors note that “even a single fasting interval (e.g., overnight) can reduce basal concentrations of metabolic biomarkers associated with chronic disease such as insulin and glucose."
The review also suggested that, unlike long fasts, intermittent fasting regimens “are not harmful physically or mentally (i.e., in terms of mood) in healthy, normal weight, overweight or obese adults.”
Risks of Prolonged Fasting
Prolonged fasts have known risks, including:
- Fatigue
- Weakness
- Headaches
- Low blood sugar
- Electrolyte abnormalities
- Nutrient deficiencies
Research continues with the goal of determining the best fasting regimens, and more research is needed to better clarify the effects of energy intake, physical activity, sleep, gut bacteria and other factors.
So, while intermittent fasting cannot be confidently recommended for long-term health benefits at this time, the possibility is one of compelling interest. Relatively simple strategies, such as minimizing night-time eating and extending the overnight fast, might represent simple new approaches to help fight disease and build wellness—giving us a new perspective on an ancient practice.
A Healthy Approach to Intermittent Fasting
So, for those who wish to try intermittent fasting, what might be a reasonable approach?
Avoid Snacking at Night
The goal is to confine your energy intake to a 12-hour time period most days of the week. For most of us, that just means avoiding night-time snacking. If your schedule allows, shift heavier intake to earlier in the day.
Stay Hydrated
Drink ample fluids during the fasting period; these can include unsweetened teas, black coffee, clear broth, plain seltzer and regular water.
Maintain a Healthy Diet
Whether fasting or not, eating a whole-foods, anti-inflammatory diet such as the Mediterranean diet remains one of the best known ways to reduce your risk of many chronic diseases.
Check in With Your Physician
Fasting is not recommended for pregnant or breast-feeding women; children; diabetic individuals on insulin; or people who have eating disorders, are underweight or who have certain other medical conditions.
Your primary care physician or registered dietitian can answer more specific questions about your particular dietary needs.
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Angela Charlton, RD-N, is a health educator with Carilion Clinic Community Health and Outreach.
