Dr Eric Berg claims a 20-hour daily fast combined with fasted High-Intensity Interval Training (HIIT) can help shift stubborn belly fat when other weight-loss methods have failed. In a YouTube video titled "How to actually lose belly fat", Dr Berg DC explained why many people struggle to shed belly fat despite "doing everything right", and outlined steps to address it.
Dr Berg specialises in healthy ketosis and intermittent fasting. He is the Director of Dr Berg Nutritionals and author of the best-selling book The Healthy Keto Plan. He no longer practises clinically, instead concentrating on health education via social media.
The 20-hour method explained
Dr Berg advocates combining a 20-hour daily fast with fasted HIIT to tackle "stubborn" belly fat. He explains that this entails going without food for 20 hours each day (or at least 18 hours), which he argues helps reduce insulin levels and unlock fat cells around the midsection.
He said: "Fasting for 20 hours a day can help lower insulin to your baseline. A HIIT workout during your fast can significantly increase adrenaline to boost belly fat loss."
During the remaining four-hour eating window, he suggests consuming just two meals with no snacking in between—for instance, a late lunch at 2pm and dinner at approximately 6pm. Dr Berg emphasises using this combined approach "when all else fails", as he maintains that conventional weight-loss methods do not produce the specific hormonal changes needed to tackle stubborn belly fat.
How HIIT can boost fat loss
To optimise fat burning, Dr Berg recommends performing brief, high-intensity HIIT workouts while still fasting. He observes that this produces a substantial surge in adrenaline, compelling the body to mobilise stubborn fat, and that it demands only 8 to 15 minutes of vigorous exercise weekly.
He added: "Weight training combined with HIIT can stimulate even more adrenaline. To reduce visceral fat, it's critical to lower insulin, which is why 20-hour fasting can be a powerful way to stimulate visceral fat loss."
The regimen also depends upon rigorous food selections and wholesome daily routines. He states you must eliminate sugars, starches, industrial palm oil and seed oils, concentrating instead on healthier fats such as olive oil.
Lifestyle factors and considerations
Dr Berg also highlights the importance of managing stress and cortisol by getting 8 hours of quality sleep, spending time outdoors in sunlight, and ceasing all food intake at least 3 hours before bedtime. He said: "There are also more cortisol receptors around the midsection than in other areas of the body, so chronic stress could be another reason you're having trouble losing belly fat."
Taking a broader look at nutrition, time-restricted eating and HIIT may help lower insulin levels and reduce visceral fat, though research indicates that your total daily calorie and protein intake remain the primary drivers of overall fat loss. Embarking on a strict 20-hour fast straight away may also leave you feeling fatigued or negatively impact your exercise performance.
Health professionals generally recommend beginning with shorter fasting windows and consulting a doctor if you have an existing medical condition or take medication that affects blood sugar levels. People with diabetes or blood sugar disorders, pregnant or breastfeeding women, people with a history of eating disorders, people with cardiovascular issues or unmanaged high blood pressure, and underweight people or those with high daily energy demands should avoid this approach.
For those who have already consulted a doctor, experts advise starting slowly with a more moderate 12:12 or 14:10 schedule to allow the body to adjust more safely. Experts also stress the importance of maintaining proper hydration and electrolyte levels, as fasting causes the body to lose water and sodium. Consuming adequate water and replacing electrolytes (sodium, potassium, magnesium) helps ward off headaches, tiredness, and muscle cramps, and exercise should be stopped immediately if chest pain, severe dizziness, confusion, or heart palpitations develop.
