Many of us experience some degree of weight gain during the winter season. Some might argue that it is because we need to eat more during winter to keep warm (not true), some say it's because we do less outdoor activities in the cold. Myth or truth, this article explored the scientific findings behind the possible cause of seasonal weight gain and the ways to compact it. The information contained in this article is also relevant to people who have mood slumps or carb cravings due to a change of environment or weather. If you fall into any of the above categories, tune in.
First thing first, yes, in general, some people are indeed more susceptible to weight gain during winter seasons. The cause of seasonal weight gain is mostly due to environmental factors, however, a possible genetic component has also been postulated. We do tend to eat more in winter, and especially crave for carbohydrate-rich foods, not because they can keep us warm, but they somehow can make us feel better. Does this sound like you? Here is why…
SAD and Co.
Yes, that's right, winter makes some of us SAD, acronym for Seasonal Affected Disorder, also known as seasonal depression. SAD is said to be "a combination of biologic and mood disturbances with a seasonal pattern", which usually occur in the autumn and winter and ends in spring and summer (Kurlansik and Ibay 2012, American Family Physician). The cause of SAD is largely due to the changes in lengths of days/nights and drop in temperatures in winter compared to summer. It's said that up to 10% of the population in the US has SAD, with a higher incidence in women than men (Miller 2005, Alternative Medicine Review). People with SAD can experience changes in mood, energy and appetite, which can result in depression, fatigue, carbohydrate consumption especially with cravings for sweats and starch-rich food and consequently result in weight gain. A study that analysed the eating habits of female SAD sufferers found that SAD patients are prone to emotional eating, thus leads to a higher chance of seasonal weight gain and a higher BMI compared to non-SAD sufferers (Krauchi 1997, Comprehensive Psychiatry).
There are a number of possible explanations for the cause of SAD, including genetic predispositions, neurotransmitter abnormalities, both sound quite serious and a bit of gibberish to most people. However, neither really explains the seasonal rhythm of SAD. I'd go and seek professional medical help if your SAD is that serious. On a more relevant note, one of the most obvious differences between summer and winter seasons, other than the change in temperature, is the shortened daylight period, which will consequently affect a person's circadian rhythm (biological clock) (to learn about the circadian rhythm and BMI please read the Dec 2012 issue of Fit Lifestyle magazine). You don't really need to have clinical SAD to experience similar symptoms, and below are what I personally think is relevant to an average Joe like you and me that suffers seasonal mood and weight changes.
The slight change in circadian rhythm will alter the production of melatonin, an endocrine hormone and a powerful antioxidant produced by the pineal gland into the blood. As the production of melatonin is kick-started by darkness and inhibited by light, it can be affected by the shortened daylight of winter. It was found that there is a delay in melatonin secretion in response to darkness in clinical SAD sufferers, and there is a difference in melatonin secretion pattern/levels in SAD patients as compared to normal people (Miller 2005, Alternative Medicine Review). A trial of 58 SAD patients were given high-dose of slow-release melatonin and a significant improvement in quality of sleep and vitality were observed, however melatonin therapy had no effect on mood (Leppamaki et al, 2003, European Neuropsychopharmacology). Go and see your doctor if you suspect you have melatonin issues.
One cannot talk about mood changes without mentioning serotonin, a hormone that controls you mood, appetite and sleep. Inadequate levels of serotonin in the brain can cause carbohydrate cravings. Serotonin has also been found to be a controller of body weight by regulating the body's energy balance. Brain serotonin levels are relevant not only to SAD sufferers, but also to anyone who has mood swings associated with environmental or weather changes. For those who feel the cravings for carbs, it may be caused by inadequate serotonin levels in your brain. The best natural ways to increase serotonin levels, according to Young (2007, Journal of Psychiatry and Neuroscience) are:
- Exposure to bright light. Uh-Huh! We live in a bright light-deprived society, where many people spend best part of their day indoors. The lights commonly used indoors do not have enough lux (luminous flux per unit area, a way to measure light intensity) to make you secrete enough serotonin. Whereas even the outdoor light on a cloudy day could make you happier. Get outdoors as much as possible without getting sun burnt, you could be happier and lighter in the process, kill two birds with one stone as they say.
- Do exercise. It has been scientifically proven that the exercise can make you happy. It was hypothesized that the decline in vigorous physical exercise, in particular, effort based rewards compared to our ancestors may contribute to high levels of depression in the current society. Adequate exercise can increased serotonin levels and hence decrease carb cravings, and you can stay active and healthy in the process.
- Diet. There is quite a bit of incorrect information floating around about this one. As serotonin is the metabolic product of tryptophan, ingestion of purified tryptophan has been found to increase brain serotonin levels. However, ingestion of food containing tryptophan does not, as the other amino acids contained in the food will compete with the tryptophan. The popular myth that is eating high protein food such as turkey can increase serotonin level, is false; similarly, the popular believe of eating bananas, which do indeed contain serotonin can improve mood, is also false, as the serotonin contained in bananas does not cross the blood-brain barrier to get into our brains to make us happy. In order for a food to increase brain serotonin levels, the tryptophan content of the food needs to be much higher than that of other amino acids, some example of those foods are specially cultivated chickpeas and alkali-processed corns.
Some have stated that the reduced vitamin D synthesis caused by a reduction of sunlight (UV-B radiation) in winter compared to summer is one possible cause of seasonal weight gain and obesity (Foss 2009, Medical Hypothesis). This seems reasonable and indeed, low vitamin D status has been linked with an increased risk of weight gain and obesity. Vitamin D is thought to play a role in adipocyte (fat cell) death and genesis as well as lipid metabolism (Song and Sergeev 2012, Nutrition Research Reviews). However, taking vitamin D (often along with calcium) doesn't seem to make you thinner, as clinical intervention trials using vitamin D yielded controversial results. There is no concrete scientific evidence in humans to indicate supplementation of vitamin D can prevent obesity in real life situations, yet.
Some may also argue that vitamin D deficiency is associated with depression and can lead to "emotional eating" and hence weight gain. Well, believe it or not, that is also a myth, well, more like an exaggerated truth. Yes, there is an association between low vitamin D levels and depression however, there is currently insufficient evidence to say that vitamin D deficiency is the antecedent cause or consequence of depression (Parker and Brotchie 2011, Acta Psychiatrica Scandinavica). So can lower vitamin D synthesis in winter cause weight gain? Not sure about that, but in case it does, get into the sun more often and consume food or supplements that contain vitamin D will be sufficient.
It's not me, blame the genes!
There seems to be a gene linked to everything these days and weight gain is no exception. There is an established genetic component in weight related disorders such as obesity, where a percentage of people have the genes to allow them to gain weight more easily than others. This phenomenon has puzzled scientists as the survival of these weight gain genes in the human population defies the theory of "survival of fittest", there is nothing "fit" about been obese.
Two main theories have been postulated in order to explain the presence of fat gaining genes, the "thrifty gene hypothesis" initially proposed by James Neel in 1962, and the "drifty gene hypothesis" first proposed by John Speakman in 2008. Scientists supporting each of the hypothesis argued with each other about the details of what kind of selection pressure required during the history of mankind to allow these genes to survive. Let's leave that part to the scientists, what is relevant, is that, scientists from both sides agreed that there is a genetic predisposition in a population of people so that some people are more prone to weight gain than others. This genetic predisposition is kept there because historically speaking, ancient humans faced famine, seasonal shortage of food and predation (or lack of), hence needed to store fat to have the energy required for survival during periods of abundance. In a developed modern society however, for instance, Australia, there is a perpetual abundance of food, and a lack of predators that feed on us humans. What was historically advantageous for survival became the culprit for causing widespread weight gain and obesity.
So, some people are genetically prone to gain weight, big deal, because ultimately, weight management is all about calories in and calories out, the choice is yours. If you eat well and exercise adequately, there is really no reason for you to gain weight any more than other people. Think of the number of calories required per day as the speed limit, and to have the "fat gene" means you have a relatively faster car than the average shopping trollies found on roads. It's easier for you to speed if you put your foot down, but there's no excuse, watch the speedometer and exercise discretion, you are more than capable of staying within the limit. It may be is the genes, but it is definitely up to you.
The purpose of this article is to show the scientific understandings behind seasonal weight gain, mood slumps and emotional eating. Not to succumb to the food cravings, instead, continue to eat healthy, spend more time outdoors and do adequate exercise, are probably the most effective natural cures to deal with these kinds of problems. It is all in your hands.