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Is Intermittent Fasting Safe & Effective for Weight Loss?

Person with plate of food looking at watch

Intermittent fasting is an eating plan that focuses on “when” you eat instead of “what” you eat. Calorie counting isn’t required and no foods are totally off limits. Instead, you only eat within a specific window of time each day and fast for the remaining hours. Many people wonder, is it the perfect diet?

“If there are no medical contraindications, I support those who want to try intermittent fasting,” says University Hospitals registered dietitian, Renee Cooper, RD, LD. “However, I typically discuss the pros and cons of fasting and advise people to proceed with caution. Sometimes, extreme fasting can create more negative outcomes than positive.”

How Does Intermittent Fasting Work?

Studies have shown that intermittent fasting can help people lose weight, prevent disease, slow aging, reduce markers of inflammation (C-reactive protein), stabilize blood sugar levels and support healthy immune function.

When the body goes for hours without food, it exhausts its sugar stores and starts burning fat for energy. This transition is called metabolic switching. It puts the body into autophagy – a state in which the body repairs itself at a cellular level to reduce inflammation and boost the immune system. Autophagy also releases the hormone glucagon, which helps manage blood sugar and is a natural appetite suppressant.

“Fasting also gives your digestive tract time to rest,” says Cooper. “Without proper rest and renewal, the barrier formed by these cells can begin to break down and leak – a condition known as leaky gut.”

Limiting eating to a specific timeframe may also have a psychological effect – helping to replace mindless eating and snacking with more purposeful eating.

Women: Proceed With Caution

Even though some research supports the health benefits of fasting, there are some cautions. Fasting for more than 12 to 14 hours a day can stress the body, increasing inflammation and levels of the stress hormone cortisol.

“Additionally, prolonged periods of not eating may slow your metabolism and lead to overeating when you’re not fasting. This could result in weight gain, increased inflammation and disrupted hunger cues,” says Cooper.

“I’m particularly hesitant to recommend intermittent fasting to women, especially women who are already stressed, not sleeping enough or chronically undereating. Most studies of intermittent fasting have been conducted on men. Therefore, the benefits for women are unclear and more research is needed.”

Intermittent fasting is also not ideal for highly active individuals, particularly those who exercise in the morning. Fasting prevents you from refueling with carbohydrates and protein within the “golden window” of 45-60 minutes after a workout to support the body’s recovery process.

Types of Intermittent Fasting

There are several types of intermittent fasting schedules that may be tried. Many people experiment to find the one that works best for their body and their lifestyle. Common schedules include:

  • 18/6: Eating during the same 6-hour window each day and fasting for the remaining 18 hours.
  • 16/8: Eating during the same 8-hour window each day and fasting for the remaining 16 hours. .
  • 12/12: Eating for 12 hours and fasting for 12 hours. .

All intermittent fasting plans have the potential to help you lose weight. However, some studies suggest that the 12/12 plan is the safest, most sustainable eating pattern.

Healthy Food Choices Are Still Important

Regardless of the plan you choose, it’s important to make healthy choices when you do eat. You should avoid highly processed foods, which are often high in added salt and sugar and have minimal nutritional value.

Instead, fill your meals with leafy greens, healthy fats, lean protein and complex, unrefined carbohydrates such as whole grains. “I recommend that people work with a dietitian to ensure they are getting adequate amounts of protein and fiber during their allotted eating window,” says Cooper.

Drink plenty of fluids throughout the day, including when you’re fasting. Black coffee and tea; water flavored with lemon, lime, cucumber or mint; and artificial sweeteners with zero carbohydrates may be enjoyed without breaking your fast.

Talk to Your Health Care Provider

Talk to your healthcare provider before starting any dietary regimen. Intermittent fasting isn’t recommended for children under 18, pregnant or breastfeeding women, and those with certain medical conditions, such as:

  • Diabetes, particularly insulin-dependent type 1 diabetes
  • A history of eating disorders like anorexia or bulimia
  • Kidney stones, GERD or other digestive disorders

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University Hospitals has a team of clinical dietitians with the expertise to provide counseling and personalized eating plans for anyone looking to enhance their health, meet nutritional goals or lose weight safely and effectively.