For we all like figgy pudding,
We all like figgy pudding,
For we all like figgy pudding,
So bring it right here.
Surely not everyone likes figgy pudding? I don’t even know what figgy pudding is. Whatever your thoughts - we all know that this is a time of year for families, for gift giving and for feasting. It is also a time when our clothes fit a little tighter and (because we live in a fat phobic culture) we tend to feel bad about this. But you know what. Most people lose their winter weight in spring or summer. So what is going on?
Oh. And I am not a nutritionist. it is beyond my remit to give nutrition advice. I’m just a reader and really curious. This blog is brimming with links to the papers that my points have come from. Please do click on them to read more.
So. Why do we put on weight over winter? There are many theories. The first one makes the most sense to me:
There’s an idea called the ‘thrifty gene hypothesis’. It proposes that as the days grow shorter our body prepares itself for cold and for food scarcity by holding onto body fat. Researchers from the University Of Exeter, explain that we have two conflicting needs. We have a desire to eat (and gain weight) for energy while avoiding starvation, and a desire to not eat so much that we are vulnerable to predators. Using computer modelling they show the desire to fight against starvation is far greater than the desire to prevent overeating. This is heightened when food is traditionally more scarce over winter, so we're more susceptible to our evolutionary urges during these times.
Another theory is that we slip into -
2) Hibernation Mode
Melatonin is another little contributor to our absence of desire to go exercise outside in the cold and dark but instead to stay indoors and hunker down. Over winter our pineal glands respond to lack of sunshine by producing the hormone melatonin. Melatonin is a messenger that tells the body to shift from active to resting metabolic function and is often called the sleep hormone.
Melatonin also modulates the action of several key metabolic hormones such as insulin, ghrelin and leptin. These hormones trigger feelings of appetite, satiety, calorie uptake and fat storage.
3) Keeping Warm Burns Energy
I know that I’ve just said that our metabolism slows over winter but it works harder too. We burn more energy when we are cold and our body requires more fuel to keep up with the metabolic demand.
And while I’m talking paradoxically -
4) Fat keeps us from getting sick
In Carl Lavie’s book: The Obesity Paradox he explains why body fat is good for immunity.
He points out that fat holds immunity boosting pre-adipocytes that devour germs and bacteria.
It stores glucose and saves energy for when we need it. It is necessary for the production and metabolising of a huge array of hormones. And importantly, fat combined with muscle mass will help us live longer if we are hit with a chronic illness.
5) Eating Warm Us Up
When our body is metabolising food it generates heat, meaning our bodies may naturally crave more food to help heat us up. Eating is a way to raise body temperature and so when cold, we seek out food where we ordinarily may not. This "thermostatic hypothesis" of eating is that we eat to keep us warm and the energy content of the food does not determine when we stop eating, instead it is the heating effect that provides a “regulatory mechanism.” Essentially keeping warm is an important physiological concern and eating provides a major contribution to maintaining body heat.
6) We Comfort Eat
I love a crisp winter’s day when the sky is blue. The thing about London though is we have many grey wet days in winter. This is hard. Many people develop a lower level of happiness, called ennui.
Studies show that when we’re suffering with ennui, we use comfort foods as a pick-me-up. Not a surprise I know. What is quite surprising is -
7) Absence of Sunshine
Researchers from the University Of Alberta, have discovered that our bodies' fat cells may have a positive reaction to sunlight. When fat cells are exposed to blue light (which the sun produces) they shrink. The researchers propose that lack of sunlight, can increase the cells' ability to store fat.
Preliminary studies also suggest that people with low levels of vitamin D store more fat, though the precise mechanism is still being identified. It might be that lack of vitamin D reduces fat breakdown and triggers fat storage, so the calories consumed are stored in adipose (fat) cells rather than being used for energy.
These are a bunch of reasons why we put on weight over winter. What happens then over spring and summer?
There is a thing called a set-point theory in regulation of body weight. This explains why we keep a relatively stable weight over long periods of time. Though we put on weight over winter it kind of just goes over summer. (well lots of technical things happen to do with the hypothalamus and an “equilibria achieved by regulation of many parameters.”)
A biological control of body weight has been observed in animal studies and with rural Gambian women.
It might be that you’ve seen it for yourself though? If not with your body, with your children? When children are ill they might not eat for days and then when they are well again - boy they are ravenous. Over winter we eat more, over summer we eat less. This is why we stay more or less the same weight. Don’t feel guilty for eating more at this time of year. Our feasts unite families and communities, they feed our spirits as well as our bodies. Don’t reject them over a fear of gaining weight.
Good tidings we bring
To you and your kin;
We wish you a merry Christmas
And a happy New Year!
And: some holiday reading ideas for you on this subject are -