Intermittent Fasting 101: What Works and What Doesn’t

While short-term fasting has notable benefits, its long-term effects and potential downsides remain a topic of discussion in the scientific community.

As a nutritionist, I want to provide an objective view: What works, what doesn’t, who should (and shouldn’t) try IF, and how to do it safely.

What is Intermittent Fasting?

Intermittent fasting is an eating pattern that cycles between fasting and eating periods. Unlike traditional diets that focus on what to eat, IF focuses on when you eat. The idea is to extend the time your body spends in a fasted state to optimize fat burning, metabolic function, and cellular repair.

Popular IF Methods:

• 16:8 – 16-hour fast, 8-hour eating window (most common).

• 5:2 – Eating normally for 5 days, restricting calories (500–600 kcal) for 2 non-consecutive days.

• OMAD (One Meal a Day) – Eating only one meal per day (more extreme).

• Alternate-Day Fasting – Fasting every other day with minimal calorie intake.

• 12:12 – A beginner-friendly method with a 12-hour fast and a 12-hour eating window.

The Benefits of Intermittent Fasting

 Weight Loss & Fat Burning

• IF helps reduce overall calorie intake, leading to weight loss (Varady et al., 2013).

• During fasting, insulin levels drop, allowing the body to access stored fat for energy (Mattson et al., 2017).

 Improved Insulin Sensitivity & Blood Sugar Control

• IF can lower fasting blood sugar and improve insulin function, making it beneficial for individuals with insulin resistance (Patterson et al., 2015).

Boosts Cellular Repair & Autophagy

• Fasting triggers autophagy, a process where the body removes damaged cells and regenerates new ones (Yoshinori Ohsumi, 2016, Nobel Prize in Medicine).

Supports Heart Health

• Studies show IF can reduce LDL cholesterol, triglycerides, and inflammation markers, lowering heart disease risk (Tinsley & La Bounty, 2015).

Potential Brain Health Benefits

• IF may protect against neurodegenerative diseases by reducing oxidative stress and inflammation in the brain (Longo & Mattson, 2014).

The Downsides of Intermittent Fasting

While IF has clear short-term benefits, it’s important to acknowledge its limitations and potential risks, especially with long-term use.

IF Can Be Hard to Sustain

• Many people struggle with hunger, irritability, or fatigue, making it difficult to stick with IF in the long run (Gabel et al., 2019).

• Social situations (family meals, dining out) can be challenging when following strict fasting schedules.

Potential Negative Impact on Metabolism Over Time

• Short-term fasting can increase metabolic rate, but prolonged fasting or excessive caloric restriction may lead to metabolic slowdown (Heilbronn et al., 2005).

• Chronic IF might lower thyroid function (T3 hormone), potentially affecting energy levels and weight management (Horne et al., 2013).

Risk of Nutrient Deficiencies

• Restricting eating windows may lead to inadequate intake of essential nutrients, especially if not planned well (Patterson et al., 2015).

• Risk of deficiencies in iron, calcium, magnesium, vitamin D, and protein if meals are not balanced.

Increased Stress & Cortisol Levels

• Fasting can elevate cortisol (stress hormone), which may lead to increased cravings, anxiety, or even fat storage (LeCheminant et al., 2013).

• Those with high stress levels or adrenal fatigue may find IF counterproductive.

May Disrupt Hormonal Balance (Especially for Women)

• IF can affect reproductive hormones, potentially causing irregular periods, low libido, and fertility issues in some women (Rothschild et al., 2014).

• Women are more sensitive to fasting-related stress, which can disrupt estrogen and progesterone balance (Vitale et al., 2021).

Not Suitable for Everyone

• Not recommended for:

  • Pregnant or breastfeeding women.

  • People with a history of eating disorders (risk of disordered eating behaviors).

  • Individuals with diabetes or low blood sugar (risk of hypoglycemia).

  • People with thyroid disorders (can slow thyroid function over time).

How to Do Intermittent Fasting Safely

If you decide to try IF, here are some tips to make it safe and sustainable:

1. Start Slow: Begin with a 12:12 or 14:10 fasting schedule before jumping into 16:8 or longer fasts.

2. Stay Hydrated: Drink plenty of water, herbal teas, and black coffee (without sugar or milk) during fasting periods.

3. Eat Nutrient-Dense Foods: Prioritize protein, healthy fats, fiber, and complex carbohydrates during your eating window. Avoid ultra-processed foods.

4. Listen to Your Body: If you feel dizzy, lightheaded, or extremely fatigued, adjust your fasting window or stop fasting.

5. Plan Your Meals: Ensure you get enough vitamins and minerals by including lean protein, leafy greens, whole grains, and healthy fats in your diet.

6. Don’t Overeat After Fasting: Avoid binge eating or overcompensating during your eating window, as this can negate the benefits of IF.

7. Consider Your Hormones: Women, in particular, should monitor their cycles and energy levels. If fasting causes menstrual irregularities or extreme fatigue, reconsider the approach.

8. Be Flexible: IF should complement your lifestyle, not control it. Modify your schedule based on your energy needs, workout routine, and social commitments.

   
   

Intermittent fasting can be a powerful tool for weight management, metabolic health, and cellular repair, but it’s not a magic bullet. It works best when combined with a nutrient-dense diet, regular exercise, and mindful eating habits.

While short-term IF can enhance metabolism, long-term excessive fasting may lead to metabolic slowdown, hormonal imbalances, and stress-related issues. The key is to personalize IF based on your body’s needs and not force a rigid approach.

Before making major dietary changes, consult with a nutritionist or healthcare provider, especially if you have pre-existing conditions.

References

• Mattson MP, Longo VD, Harvie M. (2017). "Impact of intermittent fasting on health and disease processes." Ageing Research Reviews.

• Patterson RE, Sears DD. (2015). "Metabolic effects of intermittent fasting." Annual Review of Nutrition.

• Gabel K, Hoddy KK, Haggerty N, et al. (2019). "Effects of time-restricted feeding on body weight and metabolism." Obesity.

• Heilbronn LK, Smith SR, Martin CK, Anton SD, Ravussin E. (2005). "Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism." American Journal of Clinical Nutrition.

• Rothschild J, Hoddy KK, Jambazian P, Varady KA. (2014). "Time-restricted feeding and metabolic health." Nutrition Reviews.

• Vitale R, Kim Y. (2021). "Intermittent fasting and female reproductive hormones." Endocrinology & Metabolism.

• Tinsley GM, La Bounty PM. (2015). "Effects of intermittent fasting on body composition and clinical health markers in humans." Nutrition Reviews.