Intermittent Fasting & Hormones: What’s Safe And What’s Not - Dr. Mridul Bera

Intermittent fasting has become very popular in recent years, especially among people trying to lose weight or improve their health. It involves having set hours for eating and longer periods when you don’t eat at all.

Many diets focus on what to eat, but intermittent fasting is all about when you eat.

There are several common types of intermittent fasting, including:

• Alternate-day fasting – eating one day and fasting the next

• Modified alternate-day fasting – eating very small amounts on fasting days

• 5:2 fasting – eating normally for five days and very little on two days

• Time-restricted eating – eating only within a set time window each day²

Intermittent Fasting: Benefits and Risks

Research shows that intermittent fasting doesn’t just help with weight it triggers a “metabolic switch” that can benefit the body and brain. Supporters of intermittent fasting believe that giving the body a break from constant eating helps improve insulin levels, support hormone balance, and allow the body to repair itself. It:

• Supports brain health – May improve memory and thinking skills

• Protects the heart – Can lower blood pressure and resting heart rate

• Helps with weight loss – Promotes fat loss while preserving muscle

• Improves diabetes control – May lower fasting sugar, insulin levels, and insulin resistance

• Reduces inflammation – Helps protect organs from long-term damage

• Supports cell repair – Animal studies show better healing and tissue protection^1,3

However, it is important to note that intermittent fasting is not for everyone. Some people may experience:

• Headache, fatigue, or irritability

• Constipation or dizziness

• Strong hunger leading to overeating

• Blood sugar swings, especially in people with diabetes

• Too much weight loss in older adults or underweight people^2,3

How Intermittent Fasting Affects Hormonal Health

Research suggests that intermittent fasting may help reset the body’s natural daily rhythm (also called the circadian clock). This rhythm plays a major role in keeping hormones balanced. Fasting periods can improve how insulin works, which helps control blood sugar, and may also influence thyroid hormones, stress hormones like cortisol, and sex hormones.⁴

As far as reproductive hormones are concerned research shows that:

• In women with obesity, intermittent fasting may lower testosterone-like hormones while increasing a hormone-binding protein (SHBG). This can be helpful for women with PCOS, where high testosterone causes irregular periods, acne, and fertility problems. These effects are stronger when meals are eaten earlier in the day.

• In men, intermittent fasting has been found to slightly lower testosterone in young, active individuals. However, muscle strength and physical performance were not affected. Still, lower testosterone over time could impact energy, mood, and libido.⁵

Intermittent fasting may also improve gut health. A healthier gut supports better hormone balance and reduces inflammation, which is linked to conditions like diabetes, heart disease, and even some cancers.⁴

Is Intermittent Fasting Safe?

Intermittent fasting is popular for weight loss and health, but it isn’t right for everyone. While some people use it to manage conditions like high cholesterol, arthritis, or digestive problems, fasting can be risky for certain groups.¹

You should avoid intermittent fasting if you are:

• Under 18 years of age

• Pregnant or breastfeeding

• Living with diabetes or using insulin or have frequent low blood sugar

• Recovering from or having a history of eating disorders

• Take medicines for blood pressure, heart disease, or that must be taken with food

• Are elderly, underweight, or have a long-term illness^2,3

If you feel dizzy, anxious, nauseous, or unwell after starting intermittent fasting, stop and speak with your doctor.