Fasting & Exercise Benefits

Through the principle of hormesis and the cellular stress response we can substantially improve overall health, immunity and brain function by practicing:


  • Caloric restriction (e.g.  alternate day fasting or the 5:2 diet)
  • Exercise (aerobic, resistance and/or high intensity interval training



General Health Benefits from Fasting and Exercise

Numerous intervention studies have demonstrated  that caloric restriction (with a maintained balanced diet) results in

  • reduced fat mass
  • increased insulin sensitivity and improves glucose metabolism
  • decreases blood pressure
  • increased heart rate variability (HRV) – a good index of overall mental and physical health
  • less oxidative damage during cell metabolism (due to free radicals) to tissues and DNA
  • less inflammation
  • better autophagy – the detoxification process whereby your cells eliminate waste material and repair themselves)
  • protection against multiple age-related diseases including cancers, cardiovascular disease, diabetes, a (amount of blood glucose is too high) and sarcopenia (degenerative loss of skeletal muscle mass)



Fasting with low animal protein diet


The life-extending effects of restricted diets found in other animals based on the adaptive cellular stress response is in large part due to the resulting lower levels of IGF-1 – a growth factor. It is known that higher levels of plasma  IGF-1 lead to more accelerated ageing and age-related diseases such as cancer, while low levels are protective. Luigi Fontana and colleagues found that caloric restriction (while maintaining nutrition) in human volunteers did not result in lowered IGF-1 levels.

But Humans tend to have high protein diets – well in excess of the recommended amount of protein of 0.8 grams per kg of body weight per day (e.g. 46 grams for the average US female and 56 grams for the average US male). Fontella and  found that reducing protein intake from an average of 1.67 g / kg / day to 0.95 g / kg / day for just 3 weeks in people practicing caloric restriction resulted in a reduction in IGF-1 by over 20%.


Avoid too much animal products

Reducing the amount of animal protein we eat to 10% of calories eaten reduces risk factors for prostate, breast, and colon cancers, and neurodegenerative diseases. A 2014 University of Southern California study looking at the diets of more than 6000 people found that for 50-65 year olds a diet high in animal protein (more than 20% of daily calories) was associated with a 75% increase in overall mortality and afour-fold increase in the risk of dying from cancer.

That is as big a risk factor as smoking. This link was largely eliminated when the protein source was plant based. This study also found that for over 65s, a higher protein diet was linked to reduced cancer and overall mortality. A sensible recommendation for health and longevity is 10-15% primarily plant based protein intake up to one’s mid 60s, increasing to a 20-25% in later years. Good non-animal sources of protein can be found here.


Anti-cancer effects of exercise, & fasting


Exercise training, decreased fat, and long-term low protein fasting are associated with low plasma growth factors and hormones that are linked to an increased risk of cancer. A low animal protein diet has additional protective effects because it is associated with a greater decrease in circulating IGF-I than high levels of exercise alone.

This diagram summarizes the adaptive response to caloric restriction or fasting that help fight cancer, adapted from this review article.


fasting cancer science



Brain Health & Performance Benefits from Fasting & Exercise


Via the same adaptive cellular stress response that improves immune function, health and longevity reviewed above, caloric restriction & exercise can promote optimal brain function and resistance to age-related brain diseases, and does so via overlapping and complementary mechanisms.

The hormesis response results in both increased neuroplasticity and cell protection – that is, both the strengthening of synapses via protein enzymes and neuron stress resistance via DNA repair enzymes, and antioxidant enzymes.

We will now look at specific brain benefits one by one. Much of this research can be found  in this Cell Metabolism review paper and this Nature Reviews Neuroscience paper.


Improved Neuroplasticity

Neuroplasticity is defined as the changes that occur in neural pathways and synapses (the communication points between brain cells)  as adaptive responses to environmental challenges, including those that are voluntary (e.g., problem solving, learning skills, competing in sport) and those that are unwelcomed (e.g., a traumatic injury or disease).  Neuroplasticity is essential for learning and memory, and as the brain ages it tends to become less neuroplastic.

Caloric restriction and exercise promote the functional capabilities of the brain via actions on synapses and neural stem cells, increasing neuroplasticity.


Neurogenenesis: The growth of new brain cells


Neurogenesis is the creation of new brain cells (neurons) from  neural stem cells. The new neurons can  form synapses with existing neurons, thereby becoming part of a functional neural circuit.



Improved gene regulation

Going without food for even short periods of time switches on a number of ‘repair genes’.



Ketones – Superfuel and protection for the brain

Our biology is adapted for times of food scarcity. During these periods, the main goal of our system is to provide enough glucose to the brain and other tissues. If you’re not eating where does this glucose come from? Lack of food causes the brain to shift away from using glucose as a fuel to using ketones.  Ketones are produced when the body burns fat for fuel. Ketones act as a stand in for sugar in the brain. By reducing the body’s need for sugar, less protein is required, protecting muscle mass (the protein reservoir that might otherwise be used to power the brain).



Resilience to stress and emotional control


Keeping the aging brain young: Stress reactivity

Heightened susceptibility to stress (‘stress reactivity’) increases with aging. It is associated with atrophy of the hippocampus, age-related cognitive deficits such as memory loss, and increased risk for Alzheimer’s disease.



Keeping the aging brain young: Neuroplasticity and brain function


Numerous studies show that both exercise and caloric restriction help maintain brain volume and buffer against loss of memory and other cognitive functions that is associated with loss of neuroplasticity with aging.



What Diet?

Intermittent Fasting (IF)

Research shows that the same health giving and brain enhancing genetic pathways and biochemical responses activated by caloric restriction are similarly engaged by fasting, even for relatively short periods of time.

There are two popular varieties of intermittent fasting:


Alternate Day Fasting (ADF)

This requires eating what you want one day, then cutting down to a quarter of your normal calories the next. It does not seem to matter that much what you eat on non-fast days, provided your animal protein intake is not higher than 10%. Dr Krista Varady of the University of Illinois at Chicago carried out an eight-week trial comparing two groups of overweight patients on ADF. She observed: “If you were sticking to your fast days, then in terms of cardiovascular disease risk, it didn’t seem to matter if you were eating a high-fat or low-fat diet on your feed (non-fast) days”.


5:2 Diet

This is a less intensive and often more practical version of ADF.  Five days a week you eat normally (within recommended protein limits) and then for two days a week what you do is you cut down to a quarter of your normal calories as in ADF.

The 5:2 diet has been popularized by the Michael Mosley in the BBC Horizon program Eat, Fast and Live Longer (also given a BBC feature here).  The feature is well worth a watch for an introduction to the science between restricted diet and intermittent fasting.


Mosley intermittent fasting

Michael Mosley having his health assessed before starting his 5:2 intermittent fasting diet. Click for video.


Recipes for 500-600 calorie intermittent fasting (ADF)


I recommend Michael Mosley’s very affordable book The Fast Diet if you want a practical plan for adopting alternate day fasting or the 5:2 diet.  You can download it in an instant to your Kindle. Examples of the fasting day diets are:

Fast Diet



Breakfast: 1 boiled egg, half a grapefruit (125 calories)
Dinner: vegetarian chilli (378 calories)

Breakfast: Porridge with blueberries (197 calories)
Dinner: Chicken stir fry (306 calories)

Breakfast: strawberry smoothie (171 calories)
Dinner: Oven-baked smoked haddock (325 calories)



What Exercise?

Aerobic or resistance exercise

Most of the benefits reviewed above are based on aerobic exercise, not strength training. Some studies show greater benefits of aerobic training compared to resistance (strength) training. For example



However,  this excellent article on the benefits of exercise reviews diverse evidence for the cognitive benefits of strength training among the elderly, and  suggests that while evidence is limited for the benefits of strength training, this may be due in part to lack of studies – not something intrinsic to the type of exercise.   The 2008 Physical Activity Guidelines for Americans and the Harvard School of Public Health recommends that healthy adults get:



Intensity is good


Intense exercise changes the body and muscles at a molecular level in ways that milder physical activity doesn’t match as reviewed in this New York Times feature.



High Intensity Circuit Training (HICT)


Scientific evidence indicates that high intensity circuit training (HICT) – the combines aerobic and strength training – is an efficient means of exercise to help decrease body fat, improve insulin sensitivity, and improve VO2max and muscular fitness. Interval training requires extremely intense activity intermingled with brief periods of recovery. This intermittently triggers the adaptive cellular stress response in a very efficient way.


There’s very good evidence” that high-intensity interval training provides “many of the fitness benefits of prolonged endurance training but in much less time.Chris Jordan, the director of exercise physiology at the Human Performance Institute in Orlando, Fla.  


Work by scientists at McMaster University in Hamilton, Ontario, and other institutions shows, for instance, that even a few minutes of training at an intensity approaching your maximum capacity produces molecular changes within muscles comparable to those of several hours of running or bike riding.

The ‘7 minute workout’ has  been reviewed in the New York Times, and is a popular HICT option.  There are 12 exercises. Exercises are performed for 30 seconds, with 10 seconds of transition time between bouts. Total time for the entire circuit workout is approximately 7 minutes. The circuit can also be repeated 2 to 3 times, depending on time and fitness level. Variations on this workout.


7 minute workout

The side plank (no. 12) should be done on both sides. Modifications or extensions to this routine can easily be improvised – for instance, adding pull-ups or burpees.


Combinations of Fasting, Exercise and Brain Training


How should we combine caloric restriction, exercise and brain training? There are no studies showing that exercise while fasting is detrimental to health and performance, so various combinations can be experimented with – such as:


  • Alternate Day Fasting with a daily exercise period, or exercising on either fast days or non-fast days.
  • 5:2 fasting, exercising during the non-fast days.



Brain training can be incorporated in similar overlapping or non-overlapping intervals, aiming at a total of perhaps 1 to 2 ½  hours working memory brain training per week, depending on intensity.   Your training mix should be based on reading your own energy levels and harnessing natural energy rhythms in my experience. As shown in the hormesis response diagram below, you have to experiment to ensure that you do not go into the ‘excessive stress’ zone. This is particularly true at the beginning of your training before you have built up more stress tolerance.


Hormesis response

Ensure that you do not overstress your brain and body’s biochemistry by combining multiple energetic stressors (fasting, exercise and brain training – perhaps also with stress in your work) all within the same short period.  In principle, however, if it feels right, combinations may have a synergetic benefits from the net adaptive cellular stress response.