One concern about intermittent fasting is that the body will go into “starvation mode.” Starvation mode is also known as a starvation response, famine response, and adaptive thermogenesis.
In starvation, there is no food available. Examples will be incarceration in concentration camps or prolonged famine. Fasting is when there is food, and you choose not to eat either for religious or health reasons. There is control. You can stop fasting anytime you want.
The concern about the starvation mode is that the body will:
- Decrease the metabolic rate, and the energy level will get low; therefore, you will not lose weight.
- Lose muscle mass, including the diaphragm.
- Fat reserves will be used up
- Death happens secondary to cardiac arrhythmia secondary to electrolyte imbalance
Metabolism is Increased
The metabolic rate during fasting is increased. That is because of the increase in the counterregulatory hormones noradrenaline, cortisol, and growth hormone. They are called counter-regulatory hormones because they counter insulin. Insulin stores energy. Counterregulatory hormone release energy in the form of glucose and fatty acids.
Alertness is Increased
During times of decreased caloric intake, the body has to use the glycogen reserves to maintain blood sugar within the normal range. Counterregulatory hormones facilitate that. And since the noradrenaline is increased, you will feel more awake and have more energy.
Muscle Mass is Preserved
The increase in the growth hormone preserves the lean muscle and increases fat burning as described in the article, Will Fasting Make My Muscles Shrink? The first 12 to 36 hours of fasting, depending on the physical activity will use the glycogen reserves in the liver and the skeletal muscle to support physical and mental requirements. Afterward, fat stores are used. The energy requirement in 24 hours ranges from about 1600 kcal (6700 kJ) to 6000 kcal (25,000 kJ), depending on what you do.
How Much Energy Reserves Does a Person Have?
A well-nourished 70-kg man has fuel reserves totaling about 161,000 kcal (670,000 kJ). Thus, stored fuels suffice to meet caloric needs in starvation for 1 to 3 months.
| Available energy in kcal (kJ) | |||
|---|---|---|---|
| Organ | Glucose or glycogen | Triacylglycerols | Mobilizable proteins |
| Blood | 60 (250) | 45 (200) | 0 (0) |
| Liver | 400 (1700) | 450 (2000) | 400 (1700) |
| Brain | 8 (30) | 0 (0) | 0 (0) |
| Muscle | 1,200 (5000) | 450 (2000) | 24,000 (100,000) |
| Adipose tissue | 80 (330) | 135,000 (560,000) | 40 (170) |
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Source: After G. F. Cahill, Jr. Clin. Endocrinol. Metab. 5(1976):398.
If you divide the fat reserves (adipose tissue), which are 135,000 kcal by 1,600 kcal, assuming sedentary activity, then you have enough energy from fat for 84 days or 12 weeks!
The example above is for a normal weighed man. If the person is overweight or morbidly obese, then the fat reserves will last a whole lot longer. But there is no need to fast that long.
Duration of Intermittent Fasting
The period for intermittent fasting can range from 12, 14, 16 to 22, and 36 hours. If a person is being treated for Type 2 or Adult-onset diabetes, and the goal is the elimination of insulin and other diabetic medications and cure diabetes, then the duration may go up to 3 days. Some people fast for seven days straight to take advantage of autophagy for cancer prevention. Plus, there is a reason it is called intermittent fasting. It means you can eat in between the fast. But this time, the body will burn what you eat instead of storing it again as fat.
The goal for the intermittent fasting is not just to have a beach body but to increase insulin sensitivity. It takes as short as two weeks to resolve fatty liver and fatty pancreas that are significant factors in hyperinsulinemia, insulin resistance, metabolic syndrome, and diabetes.
During Fasting Salt Intake must be Increased
During fasting, as the body becomes more sensitive to insulin and more urine will be produced. Sodium, magnesium, and other electrolytes will go along with the urine. That is why it is recommended to increase salt intake to prevent electrolyte imbalance. Himalayan salt is better since it contains more electrolytes compared to common table salt. Don’t worry about the increase in salt intake because studies have shown that a low salt diet based on this NHANES Study, is associated with an INCREASE in cardiovascular mortality. Yes, you read that right. That is not a typo.
Conclusion:
During intermittent fasting,
- The metabolic rate increases and make you more alert and helps burn fat.
- Skeletal muscle is preserved
- Fat stores will go down (which is good) but not get depleted.
- As long as there is an adequate salt replacement, electrolyte abnormalities are prevented
Cautionary Note: If you are on medications, especially for diabetes, hypertension, and heart disease, take to your doctor first before starting on an intermittent fasting program. Medication dose adjustments may be needed.
World Record Fasting Record
The world record duration of fasting goes to Angus Barbieri. It happened in 1965. Angus started as 207 kg (455.4 lbs) and lost 125 kilograms (275 pounds). The fasting was done under medical supervision, and Angus gets to go home. During the duration of the fast, he only had water and multivitamins. After one year and 17 days, Angus stopped fasting because he reached his target weight goal of 81 kg (180 lbs). Angus felt fine the whole time and was able to maintain his weight after one year at 196 pounds. Don’t try that at home without medical supervision. I included this unique story about Angus to exemplify that fasting is safe, even if prolonged.
Thank you to Lorraine L.E. for the question about the starvation mode.
Related Readings:
- How to Do Intermittent Fasting
- The Kaizen Way of Fasting
- The Science of Fasting
- 10 Unbelievably Easy Ways to Screw Up Intermittent Fasting!
- Will Fasting Make My Muscles Shrink?
- Are You Skipping Breakfast?
- The 20/80 Rule for Health
- Autophagy – How to Recycle Yourself
DrJesseSantiano.com does not provide medical advice, diagnosis or treatment