Intermittent fasting - what science really says
16:8, 5:2, OMAD - interval fasting is in vogue. But what does the research really say? A sober look at the opportunities and limitations.
Intermittent Fasting: Hype or Cure?
Intermittent fasting is one of the biggest dietary trends of recent years. Celebrities swear by it, biohackers are promoting it, and social media is full of before-and-after photos. But as is often the case with trends, it’s worth taking a sober look at the science.
The good news: Intermittent fasting isn’t hocus-pocus. There are real physiological effects. The not-so-good news: It’s not a miracle cure—and for some people, it’s even counterproductive.
Common methods
16:8 — the most popular model
Fast for 16 hours, eat for 8 hours. In practice: skip breakfast or eat dinner earlier. Easy for most people to follow.
5:2 — the part-time version
Eat normally for 5 days, consume only 500–600 kcal on 2 non-consecutive days. More flexible, but the fasting days can be challenging.
Alternate-Day Fasting
Fast (or eat very little) every other day. Effective in studies, but difficult to sustain long-term.
OMAD (One Meal A Day)
Just one meal a day. Extreme and not recommended for most people—high risk of nutrient deficiencies and disordered eating.
What happens in the body?
After 12–16 hours without food, your body activates some interesting processes:
- Autophagy — cellular self-cleaning. Damaged cellular components are recycled. (2016 Nobel Prize awarded to Yoshinori Ohsumi)
- Insulin sensitivity improves — lower insulin levels allow for better fat burning
- Growth hormone levels rise — up to 5 times higher after 24 hours of fasting, promoting muscle preservation and fat loss
- Fat oxidation increases — the body increasingly uses fat reserves as an energy source
- Inflammation markers decrease — especially in people with elevated levels
What the studies really show
An honest summary of the research:
- Weight loss: Intermittent fasting leads to similar weight loss as traditional calorie restriction — no more, no less
- Insulin resistance: Improvement in overweight individuals, especially those at risk for type 2 diabetes
- Inflammation markers: Reduction with certain protocols (especially 5:2)
- Cognitive function: Some animal studies are promising; human data is still limited
- Longevity: Strong evidence from animal studies, not yet proven in humans
The scientific conclusion: Intermittent fasting is one of many valid methods—but not a miracle cure.
Important note Intermittent fasting is not suitable for everyone. If you have an eating disorder, are pregnant or breastfeeding, have type 1 diabetes, are underweight or want to have children, you should definitely speak to a doctor before fasting.
Intermittent Fasting from a Psychological Perspective
This is where it gets interesting—and critical. For some people, intermittent fasting can be a diet in disguise:
- It can encourage restrictive thinking: “I can’t eat until noon”
- It can lead to overeating during the eating window: “I have to make up for everything now”
- People with a history of dieting may experience it as a new form of control
- It can suppress hunger signals instead of training them
If you try intermittent fasting, observe honestly: Does it feel liberating or controlling? Do you eat in a relaxed or rushed manner during the eating phase? If it feels like a diet—it probably is one.
For an alternative approach, read: Why Diets Fail and Intuitive Eating.
Can I drink something while fasting?
Yes - water, unsweetened tea and black coffee are allowed and do not interfere with fasting. Milk, sugar or high-calorie drinks break the fast. Bulletproof coffee (with butter/coconut oil) is controversial.
Do I lose muscle during interval fasting?
At 16:8 with sufficient protein intake and strength training, studies show no significant muscle loss. The risk increases with more extreme protocols (24h+ fasting). At least 1.6g protein per kg body weight in the eating phase is recommended.
Is intermittent fasting different for women?
Yes, women are hormonally more sensitive to fasting. Fasting for too long can disrupt the menstrual cycle in women and increase cortisol. A gentler protocol (14:10 instead of 16:8) and not fasting every day are often more suitable for women.
Can I exercise with intermittent fasting?
Yes, moderate exercise on an empty stomach is safe for most people. Intensive strength training should ideally be carried out during or shortly before the eating phase in order to optimally support regeneration.