Fat has the benefits of being fat!
Written by | Bai Jiaying
Source | "Medical Community" public account
Obesity has long been considered a risk factor for the health of the body, and today, in this era of "beauty for beauty" as the mainstream aesthetic, obese people may also face serious social discrimination.
Image source: Ruijing Creative
However, on April 25, The Team of Xiaoming Shi of the Institute for Environmental and Health-related Product Safety of the Chinese Center for Disease Control and Prevention published a 20-year prospective cohort study in the Nature sub-journal showing that overweight or mild obesity in China's older people over 80 years old is associated with reduced mortality, supporting the existence of an "obesity paradox" in China's oldest population (80 years and older).
Screenshots of research publications
The "obesity paradox" was an unexpected finding of Schmidt and colleagues at the University of Mississippi Medical Center in 1999 when processing data: the survival advantage of overweight and obese patients with kidney failure undergoing hemodialysis was more pronounced than normal weight.
Deviant "science"?
The existence of the "obesity paradox" has been found in patients with cardiovascular disease.
A previous study showed that in people aged 70 and older, the relative risk of cardiovascular disease death in overweight or obese people is much lower than in younger people. However, few studies have elucidated the potentially complex inverse association between the body mass index (BMI) and etiological-specific mortality in older adults.
BMI is a commonly used international standard to measure the degree of fat and thinness of the human body and whether it is healthy. The calculation formula is: BMI = weight÷ height 2 (weight unit: kg; height unit: meter).
A BMI greater than 25 is overweight and greater than 30 is obese. Image source: Ruijing Creative
In the study by Shi Xiaoming's team, the research team reported the relationship between the BMI and the risk of death among 27,026 elderly people in the community (mean age 92.7±7.5 years) in China from 1998 to 2018. The study provides evidence suggesting that the "normal" weight (18.5-24.0 kg/m2) of older adults may need to be redefined.
The results of the analysis of BMI and mortality showed that overweight and obesity were not significantly associated with cardiovascular mortality compared with normal body weight, but were associated with significant reductions in non-cardiovascular mortality and all-cause mortality.
Relationship between BMI and all-cause, cardiovascular and non-cardiovascular mortality in older adults. Image source: Nature Aging
At the same time, the study notes that there are other data showing that traditional cardiovascular risk factors, such as hypercholesterolemia and high blood pressure, contradict better survival rates in older adults. Given this finding, it is not surprising that overweight and obesity were not associated with an increased risk of cardiovascular disease death in this study, but rather with a decrease in non-cardiovascular disease mortality.
A more sensitive indicator of waist obesity
The research team further analyzed the association between the risk of death and waist circumference in this segment of overweight or obese people. The results showed that inversely correlateral waist circumference with all-cause and non-cardiovascular mortality was observed in both men and women. Although waist circumference was significantly associated with an increase in cardiovascular mortality in men, this association was not observed in women.
Relationship between male and female waist circumference and all-cause, cardiovascular and non-cardiovascular mortality. Image source: Nature Aging
Overweight and obesity may be an indicator of improved nutritional status, and the benefits of better nutrition outweigh the harms caused by higher BMI, which may partially explain the negative correlation between BMI and mortality. Waist circumference provides a more sensitive indicator of abdominal obesity compared to BMI and shows an increase in non-cardiovascular mortality associated with these indicators.
For the elderly in this study, the waist circumference increased and non-cardiovascular mortality decreased, which the researchers speculate may be because obesity provides protective energy reserves, protective adipokines, endotoxin-lipoprotein interactions, and/or fat toxin sequestration, resulting in a survival advantage.
It is worth mentioning that a previous meta-analysis of 19538 elderly people with a median age of 84.2 years, including 20 studies in Europe, Asia, North America and Australia, also found a negative correlation between BMI and mortality. All in all, the negative correlation between high BMI and mortality among the elderly is broadly similar not only in The Elderly in China, but also among Asians, North Americans, and Europeans.
For chinese elderly people aged 80 and above, the best BMI should be raised
The journal Nature Aging, which also published an opinion piece from Jean Woo of the University of Chinese in Hong Kong, noted that public health policy recommends keeping the BMI below 25 or else being considered overweight or obese. The study published by Shi Xiaoming's team shows that for Chinese elderly people aged 80 and over, the best BMI may be raised.
The study of older adults aged 80 and older was followed longitudinally for up to 20 years. The researchers linked BMI to all-cause mortality (and subdivided into cardiovascular and non-cardiovascular diseases) and found that the optimal BMI associated with a decline in mortality was between 26-30.6.
The best BMI of all-cause, cardiovascular, and non-cardiovascular mortality in people aged 80 years and older
In addition, the current BMI thresholds for overweight and obesity are based on epidemiological studies of ordinary adults of all ages, but Shi Xiaoming's team's study found that a lower risk of death is associated with BMI for overweight or even mild obesity, and also challenges the definition of the scope of BMI in the 80 years and older in mainland China.
It is worth mentioning that although the "obesity paradox" breaks the shackles of aesthetics to some extent, it is contrary to the original conclusion that "obesity affects health". However, in the past, it was generally believed that obesity was a risk factor for cardiovascular system diseases, diabetes, sleep apnea syndrome, metabolic diseases, endocrine system diseases, cancer, reproductive ability, mental illness and other diseases.
Therefore, a large proportion of scientists believe that the existence of this theory cannot be underestimated the harm that "obesity" may cause.
bibliography:
[1] Lv,Y.,Mao,C.,Gao,X.et al. The obesity paradox is mostly driven by decreased noncardiovascular disease mortality in the oldest old in China:a 20-year prospective cohort study. Nat Aging(2022).
[2] Whitlock,G.et al. Body-mass index and cause-specific mortality in 900 000
adults:collaborative analyses of 57 prospective studies. Lancet 373,
1083–1096(2009).
https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(09)60318-4/fulltext
[3] Lee,D.H.et al. Predicted lean body mass,fat mass,and all cause and cause
specifc mortality in men:prospective US cohort study. BMJ 362,k2575
(2018).
https://www.bmj.com/content/362/bmj.k2575
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