Temperature: In a study of more than 1500 middle-aged adults, it was found that those with the warmest homes were about twice as likely to become obese over the six-year research period. Most fat on our bodies is a type called white fat, but when temperatures drop to about 18 °C, brown fat starts burning the white fat to warm you up. Unfortunately, if you are not regularly exposed to cold, your brown fat deposits shrink and so too does your capacity to burn off that extra sweet treat.
Tip: Turn down your thermostat and be brave about having the odd cold shower or bracing swim.
Plastic packaging: Some plastic packaging and cans contain endocrine (hormone) disrupter chemicals that can leach into food and drinks, and evidence has linked these to expanding waistlines. These chemicals interfere with the normal functioning of hormones, targeting, for example, the thyroid gland which regulates our metabolic rate. In 2010, a team from Boston University reported that men with a bigger body mass index (BMI) and waist circumference had higher blood concentrations of metabolites of phthalate, while other research has linked obesity to exposure to bisphenol A.
Tip: Look out for PVC packaging – labelled “Type 3″ for recycling purposes – which can contain phthalates or bisphenol A, especially when buying fatty foods in which endocrine disrupters accumulate.
Altered circadian rhythms: Light at night can alter circadian clock genes, changing your metabolism. A trial at Ohio State University found that mice exposed to light at night weighed 10 per cent more at the end of the eight-week study than mice that had experienced a standard light/dark cycle, even though they ate the same number of calories and did the same amount of exercise.
Tip: Keep a consistent pattern of hours of light and darkness throughout the week and avoid LED blue wavelengths of light at night. These are known to be especially disruptive to the circadian system.
Air pollution: Breathing polluted air can cause extra fat to accumulate around your stomach and also make your cells less sensitive to insulin. This, as a result, increases your risk of developing type 2 diabetes. In a trial at Ohio State University young mice were exposed to air heavily polluted with fine particles for 6 hours a day, five days a week, and after 10 weeks they had about 50 per cent more abdominal fat than mice that were fed the same diet but inhaled filtered air.
Tip: Avoid exercising in polluted areas – be it a busy city street or next to a field where a farmer is crop spraying.
Stress: Brain imaging studies at Yale University showed that stress increases activity in the ventral striatum, a region in the brain associated with reward and habits. So it increases craving for high-calorie foods in those who have a habit of consuming them.
Tip: Instead of counting calories, practise stress reduction and meditation techniques to cultivate an awareness of how your thoughts/behaviours can undermine your health.