If you hate early morning jogs but love Sudokus over breakfast, it sounds ideal. But is it accurate? Neuroscientist Petra Ritter gives it some thought.
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Bernstein member involved: Petra Ritter
Robert Sapolsky of Stanford University recently claimed that while playing in tournaments chess players can burn up to 6 000 calories per day, three times the daily average.
“But this was only inferred from breathing rates, blood pressure and muscle contractions,” explains Ritter. “Although these can be as high for chess players in tournaments as athletes during exercise, it doesn’t mean the same energy is used.”
In fact Ritter points out that when measuring energy expenditure with indirect calorimetry – the standard method in exercise physiology – it was found that chess players burned an average of 1.67 calories per minute while playing chess, compared to 1.53 while at rest. A modest 10 % increase.
“It’s actually intrinsic activity for basic functioning that needs the most energy, surprisingly additional tasks such as reading require no more than 5 % extra energy,” adds Ritter.
The brain’s ‘dark energy’
It turns out that while the metabolic activity of the brain is known to be remarkably constant over time, the energy cost of intrinsic activity is still unclear, so is often referred to as the brain’s ‘dark energy’.
What is known is that while the brain comprises only 2 % of bodyweight, it is responsible for 20 % of the body’s oxygen demand while the body is at rest. It also uses 3.5 ml of oxygen per 100 g of brain tissue, about 10 times the energy consumption of other organs.
About 25 % of the brain’s energy consumption is needed for routine housekeeping, such as dealing with DNA damage, while the rest is spent on neural activity. This ratio seems to be stable across species.
“While it is true that the less brain activity, the lower the energy consumption, estimates suggest that eight hours of very hard mental work would require 100-200 extra calories,” says Ritter.
As the brain is powered almost exclusively by glucose in aerobic conditions, measuring glucose uptake offers an indirect indicator of energy demand. Using radioactively marked glucose, researchers can track changes in the brain’s oxygen consumption, complemented by neuronal activity recordings.
“This tells us that the brain’s daily energy consumption is pretty stable at about 500 calories,” remarks Ritter. Bad news for anyone hoping to think themselves thin.
The brain’s energy-saving setting
Ritter suggests the impact of fasting and exercise on the brain’s energy metabolism is a more interesting aspect of this question. With depleted glucose, alternative fuels such as ketone bodies, lactate and medium chain triglycerides are used.
“The body gets used to chronic calory restrictions with metabolic slowing, which reduces energy expenditure and oxidative stress. A 15 % reduction in calories over two years leads to approximately 80-120 kilocalories per day less energy needed than would be expected from weight loss alone,” explains Ritter.
Indeed, in the EU-funded BrainModes project, Ritter used scans of individual brains to run simulations of brain functioning, with implications for efficient learning strategies.
“The brain seems to save much energy during learning by working with short-term memory phenomena such as neuropsychology engrams,” says Ritter.
Ritter is now looking to the emerging field of ‘turbulence’ which borrows from statistical physics, thermodynamics and information theory, to offer insights about the levels of brain organisation.
“We are working towards a coherent picture of how energy creates information and then represents and transmits it across the different levels from cellular to cognitive processes. We are modelling this using turbulent dynamics,” adds Ritter.
For now it seems if you want to lose weight, you’ll still need to put down the pawn and pick up your trainers.
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