What Is the Potential for Cold Exposure as a Weight-Loss Strategy?

Cold-induced thermogenic capacity increases following cold acclimation, allowing individuals to burn more energy at a given level of thermal comfort; the average person might be capable of burning 20-30% more energy under mild cold exposure

Further to two previous posts, this post investigates the potential for cold exposure as a weight-loss strategy. As noted previously, adult humans possess metabolically active brown fat, which produces heat under mild cold exposure via non-shivering thermogenesis. Since exposure to mild cold does not induce shivering, most people may not find it too uncomfortable. Hence, it could be an effective weight-loss strategy.

There are individual differences in cold-induced thermogenic capacity, meaning that cold exposure elicits a greater adaptive response in some people than in others. Obese individuals exhibit substantially lower brown fat activity than lean individuals when exposed to cold, and at least part of this disparity is presumably due to individual differences in thermogenic capacity. Indeed, polymorphisms in the UCP-1 gene are associated with lower thermogenic responses to overfeeding, and higher body mass index. Moreover, in a recent experimental study, insertion of the UCP-1 gene into pig embryos gave rise to piglets that exhibited improved thermoregulation, elevated lipolysis and lower adiposity.

Brown fat activity is negatively related to age, meaning that cold exposure elicits a weaker adaptive thermogenic response in older people than in younger people. Indeed, brown fat was not thought to be present in human adults until recently. By contrast, human infants possess a large amount of brown fat, which plays an essential role in thermoregulation during the neonatal period.

It follows that an individual’s age and genetics put some upper bound on his thermogenic capacity (just as they put some upper bound on his physical strength). However, evidence indicates that the vast majority of people are capable of burning some energy under mild cold exposure, and that one’s capacity to do so increases following cold acclimation. In other words, an individual can be trained to burn more energy under cold exposure by gradually spending longer and longer periods outside the thermal comfort zone (just as he can be trained to produce higher force by gradually lifting heavier and heavier weights).

In a study by van der Lans et al. (2013), subjects were exposed to a temperature of ~16°C for 10 consecutive days (2 hours on the first day, 4 hours on the second day, and 6 hours on the remaining days). The subjects exhibited higher levels of non-shivering thermogenesis when exposed to mild cold after the protocol than they had done before. In addition, they judged the cold stimulus to be more comfortable, and reported less shivering. The upshot is that individuals can tolerate lower ambient temperatures following cold acclimation insofar as they are able to generate more heat via non-shivering thermogenesis (as opposed to shivering). This means they are capable of burning more energy at any given level of thermal comfort.

In another study by Yoneshiro et al. (2013), subjects were exposed to a temperature of ~17°C for 2 hours per day for a total 6 weeks. At the end of the 6-week period, they exhibited higher brown fat activity, higher levels of non-shivering thermogenesis, and ~5% lower body fat mass. Moreover, change in body fat mass was associated with change in brown fat activity across subjects, which suggests that higher brown fat activity mediated the effect of cold exposure on body fat mass.

How much more energy can an individual feasibly burn under mild cold exposure? As noted previously, Luo et al. (2016) found that average metabolic rate was ~16% higher at a temperature of 16°C than at a temperature of 26°C for individuals wearing “light clothing”, and was ~6% higher for individuals wearing “medium clothing”. Similarly, van Ooijen et al. (2004) found that average metabolic rate was ~9% higher at a temperature of 15°C than at a temperature of 22°C for individuals wearing “standard clothing”. However, there was substantial inter-individual variation in both studies. The maximum increase in metabolic rate was ~23% in Luo et al.’s study, and was ~30% in Ooijen et al.’s study.

Furthermore, since there is no reason to believe that the subjects in either of these studies were acclimated to cold, the reported increases in metabolic rate should be considered lower bounds on what could be achieved following, say, several months of cold acclimation. Indeed, Yoneshiro et al. (2013) observed a very large increase (>100%) in average metabolic rate at 19°C was following 6 weeks of cold exposure (see their Figure 3D). And according to van Marken Lichtenbelt et al. (2017), a historical analysis of Dutch newspapers revealed that an ambient temperature of ~14°C was considered comfortable circa 1870, which suggests that Europeans may have had a much higher level of cold acclimation prior to the era of central heating.

If the average person is capable of burning 10–15% more energy under mild cold exposure before cold acclimation, it seems reasonably to suppose that she might be able to burn up to, say, 20–30% more energy following long-term cold acclimation (and perhaps a greater amount). An important caveat is that many of the people who might consider using cold exposure as a weight-loss strategy probably have below-average thermogenic capacity. The reason being that those with high thermogenic capacity are unlikely to be substantially above their ideal bodyweight to begin with.

One final question to consider is whether individuals compensate for energy burned through non-shivering thermogenesis by simply ingesting more calories. According to a recent study, the answer appears to be “no”, at least in the short term. Langeveld et al. (2016) assigned subjects to one of two groups: the first group was kept at a temperature of 24°C for 150 minutes; the second group was kept at a temperature of 18°C for 150 minutes. Afterwards, subjects were permitted to eat ad lib. The authors observed small and non-significant differences in both average time spent eating and average calories ingested.

In conclusion, an individual’s age and genetics put some upper bound on his thermogenic capacity. Yet evidence indicates that the vast majority of people are capable of burning some energy under mild cold exposure, and that one’s capacity to do so increases following cold acclimation. The average person might be capable of burn up to 20–30% more energy under mild cold exposure, after long-term cold acclimation.