This myth is kept alive by the fact that, every so often, a study is published in which the mortality rate of ‘slightly overweight’ people (BMI 25 to 29.9) is found to be lower than that of people of normal weight (BMI 18.5 to 24.9). Fle- gal et al. (2013) is one of these studies.
But their research failed to take two important factors into account: firstly, smokers weigh less on average than non- smokers, which meant that the group of people of normal weight included more smokers (who had a higher risk of death due to their smoking habit); sec- ondly, a lot of people lose a significant amount of weight in the course of a se- vere illness and die with what appears to be normal body weight, even though they were overweight when they first became ill.
My grandmother is an example of this: she was severely obese, suffered a stroke, was bedridden for years, and lost a lot of weight, finally dying with her weight within the normal range. It is the conditions that are associated with obesity in particular, such as cardiovascular disease, cancer, and strokes, that often lead to severe weight loss prior to death.
When these people, i.e., those who weigh less due to illness or because of their nicotine consumption, appear in greater numbers in the group of people with normal weight, the morbidity re- sults will, of course, be skewed. If these kinds of factors are controlled, the results look very different.
Once that’s done, being even slightly overweight no longer appears to be healthier than being of normal weight, but rather more harmful.
Not harmful to the same extent as actual obesity, of course, but it’s still unhealthy. In 2006, Adams et al. investigated whether or not being ‘slightly overweight’ is harmful to health, and took into account factors such as chronic illness and smoking.
According to their analysis, the subjects’ risk of dying within the subsequent ten years after the start of the study was increased by 20 to 40 per cent among those who were slightly overweight, while for the obese it was increased by 200 to 300 per cent. It’s convincing evidence of the fact that being even slightly overweight consti- tutes a health risk.
A 2010 study of almost 1.5 million people carried out by Berrington de Gon- zalez et al. also found that people with a BMI of between 20 and 24.9 have the lowest risk of mortality. In the underweight range (BMI 15 to 18.4) the risk of death was increased by 47 per cent, placing it at a similar level to those who are slightly overweight (BMI 30 to 34.9). Severe obesity was associated with a 151 per cent higher risk of death. Calle et al. (1999) found that the BMI with the lowest risk of death among healthy female non-smokers was between 20.5 and 24.9, and for equivalent men, it was between 22 and 26.4.
A study by Manson et al. (1995) found that for women who had never smoked and weren’t underweight due to illness, the lowest risk of death was with a BMI of less than 19. A BMI of 19 to 25 meant a 20 per cent increase in the risk of mortality, compared to the average across all subjects, a BMI of 25 to 27 in- creased the risk by 30 per cent, and the increased risk for a BMI between 27 and 29 was 60 per cent.
Finally, among obese women, the risk of death was in- creased by 120 per cent. The risk of dying from cardiovascular disease was as much as 310 per cent higher for obese women than for those with a BMI of less than 19. In a 2012 interview with the German weekly newspaper, Die Zeit, the epidemi- ologist Dr Rudolf Kaaks said that even a BMI in the upper-normal range can represent a far higher risk of getting cancer than one in the lower-normal range.
This is presumably linked to the previously mentioned problem with the BMI, in that half the time it assigns harmless weight levels to people whose percentage of body fat is in fact too high. In my opinion, body-fat percentage is ultimately a more crucial factor than BMI. In large-scale studies like those quoted above, and in the studies that I quote later in the sections about individual medical conditions, a BMI at the lower end of the normal range almost always turns out to be associated with the lowest risk.
This is probably thanks to the fact that the majority of people in modern societies lead very physically inactive lives. In 2015, the British newspaper The Telegraph ran an article saying that pre- vious recommendations of 2.5 hours of exercise per week were unrealistic and too challenging, and suggesting that 20 minutes per week was a better target. In a survey on the Citimarathon blog, 60 per cent of Germans said that they did no exercise, and only 20 per cent actually exercised regularly. This must lead us to
As I already mentioned in the context of the BMI, those people categorised as overweight due to their excessive muscle mass are the absolute exception, while far too many people end up in the normal weight category simply because they have so little muscle mass. So, an average person who leads a relatively sedentary life and does little or no exercise would need to be at the lower end of the BMI scale to have the best chances of a good body-fat percentage and low risk to health.Someone who exercises and is reasonably muscular, by contrast,
can have a healthy body-fat percentage while in the mid to upper normal BMI range, or, for those who do a lot of weightlifting, even in the slightly overweight range. In general, the situation is very clear: a low percentage of body fat is the healthiest state, and for anyone who doesn’t happen to be a body builder, nor- mal weight is considerably healthier than being even slightly overweight.