When I was researching my book « The Sugar Casino », one of the questions that puzzled me was why we are consuming more calories than in the past. Referring to USDA data, I wrote,
« According to the loss-adjusted food availability data, Americans are consuming more calories per day than they did 40 years ago. In 1970, Americans consumed an estimated 2,109 calories per person per day; in 2010 they consumed an estimated 2,568 calories….
The average American is eating 459 calories more each day today than he, or his parents, were eating in 1970. »
I have now, rather surprisingly, found part of the answer to that question in « Why We Sleep: The New Science of Sleep and Dreams » by Matthew Walker, a British scientist and professor of neuroscience and psychology at the University of California, Berkeley. He was previously a professor of psychiatry at Harvard Medical School. (An article in last week’s Guardian newspaper summarised some of the main themes of the book.)
Regarding the effect that sleep has on health, particularly on obesity, Mr Walker explains that two hormones in your brain control your appetite: leptin and ghrelin. Leptin signals a sense of feeling full, while ghrelin triggers a strong sense of hunger. He writes that clinical tests have shown that « inadequate sleep decreased concentrations of the satiety-signalling hormone leptin and increased levels of hunger-instigating hormone ghrelin. »
Looking to see what this might mean in practice, one clinical test found that individuals who slept between four and six hours per night consumed 300 calories per day more than individuals who slept eight and a half hours per night. He writes, « Scale that up to a working year, and assuming one month of vacation in which sleep becomes abundant, and you will have consumed more than 70,000 extra calories. Based on calorific estimates, that would cause 10 to 15 pounds of weight gain a year. »
But it is not just a question of how much you eat, but also what you eat. Sleep loss increases the levels of endocannabinoids which, like marijuana, can give you the « munchies ».
In one test, participants were given access to an unlimited lunchtime buffet. « Despite eating almost 2,000 calories during the buffet lunch, sleep-deprived individuals dove into the snack bar. They consumed an additional 330 calories of snack foods after the full meal, compared to when they were getting plenty of sleep each night. »
Tests also found that sleep deprived individuals were 30 to 40 percent more likely to have cravings for sweets, carbohydrate-rich foods, and salty snacks compared to protein-rich foods such as meat or fish.
And Mr Walker counters the argument that your body needs more calories the less it sleeps. He writes, « Sleep, it turns out, is an intensely metabolic active state for body and brain alike. » What’s more, the less you sleep, he argues, the less active you will be during the day. He writes, « inadequate sleep is the perfect recipe for obesity: greater calorie intake, lower calorie consumption. » He continues,
« Of course, the obesity epidemic that has engulfed large portions of the world is not caused by lack of sleep alone. The rise in consumption of processed foods, an increase in serving sizes, and the more sedentary nature of human beings are all triggers. However, these changes are insufficient to explain the dramatic escalation of obesity. »
To emphasise the point, Mr Walker plots the reduction in sleep time (dotted line) over the past 50 years in the US on the same graph as the rise in obesity rates (below).
He summarises the current state of scientific research as follows: « Short sleep (of the type than many adults in first-world countries commonly and routinely report) will increase hunger and appetite, compromise impulse control within the brain, increase food consumption (especially of high-calorie foods), decrease feelings of food satisfaction after eating, and prevent effective weight loss when dieting. »
And as a warning for future generations, he argues, “We are now observing these effects very early in life. Three-year-olds sleeping just ten and a half hours or less per night have a 45 percent increased risk of being obese by age seven than those who get twelve hours sleep a night. To set our children on a pathway of ill health this early in life by way of sleep neglect is a travesty”
Going back to my original question, it is possible that changing sleeping habits explain 300 of the more than 450 extra calories that we consume each day compared to our parents. The rest, I imagine, can be explained by the greater availability of calorie-rich processed foods and larger portion sizes.
So if after a long night entertaining customers you are now reading this blog on your telephone while trying to stay awake at the back of a conference hall, let yourself drift off. It may mean you eat less at the conference lunch buffet!
Interesting scientific finding, although I can’t help but think, that if you are asleep, eating is rather challenging, and if you are awake and not active or on the go, the urge to nibble is quite strong.
Iwill have to reread Rip van Winkle and Sleeping Beauty to see if they shed kilos during their prolonged naps