If you thought that the stresses of present-picking, turkey-basting and relative-juggling are to blame for weight gain, you are not alone. A Google search for ‘stress and weight gain’ reveals a staggering 32,000,000 sites dealing with the topic. However, researchers from our research group have shown that the effect of stress on weight gain may not be as large as you may have thought.
The body tries to maintain stability by adapting to a change in the environment, a process called homeostasis. Stress can be defined as any external factor, physical or psychological, which threatens to throw the body out of homeostasis. Whether running from a hungry lion, or suffering stage-fright before a speech, the body’s response will be the same: the stressor (lion or stage-fright) will trigger the so called ‘fight-or-flight-response’, which is marked by increased heartbeat, muscle-tension, sweating, dilation of the pupils and the release of the ‘stress-hormones’ adrenalin and cortisol. This response is extremely useful to mobilise resources, help us get through difficult situations and regain homeostasis. However, when we experience the on-going stresses of modern life, such as money-worries, job stress, or social pressures, we begin to feel the strain. Long-term stressors overwhelm the body’s coping system, deplete resources and ultimately lead to exhaustion. It has been thought that weight gain results from the body trying to restore homeostasis by inducing metabolic changes which promote fat storage on the one hand and behaviour changes on the other, for example making less time to be active or reaching for cookies instead of carrots.
Results from studies investigating this topic are mixed – some have found that stress has an effect on weight gain, and others have not. Researchers from our department decided to look at the effect from all these studies overall. Summarizing results of several studies on the same topic to find out the ‘true’ effect is called meta-analysis. The studies that were included in this meta-analysis had to be conducted over a period of time (because these are more accurate than studies that only look at a single time-point), measure weight objectively, and focus on external stressors such as life events, work-or caregiver stress. Fourteen studies from Europe and the USA met the criteria; each ‘stress category’ (life events, work- or caregiver stress) was analysed separately.
Results of the meta-analysis showed that stress is related to weight gain, although the effects were very small. When the researchers looked at the results in more depth, they saw that studies that went on for longer and were of better quality were more likely to show an effect of stress on weight. They also saw that the effect appeared to be stronger in men. It did not matter whether the stressor was related to life or work. Unfortunately, eating behaviour was not assessed, so the researchers could not tell whether it changed under stress.
Although there are not very many studies that looked at the topic over a period of time, and imprecise measurements of stress were often used, the findings are relatively robust because of the way the studies were combined. Finding a stronger link of stress on weight in men complements other findings which show that men have a stronger fight-or-flight response. Overall, however, it can be seen that the effects of stress on weight are much smaller than often made out in the media. Blaming the relatives for a bulging belly might be convenient, but complex issues like weight gain unfortunately have no simple, or convenient, answer.