UK study suggests under 45s and women more likely to gain weight and jump a BMI category during lockdown

New research being presented at this year's European Congress on Obesity (ECO) in Maastricht, Netherlands (4-7 May), suggests that most adults in the UK did not lose or gain enough weight following the first pandemic lockdown to change their body mass index (BMI) category, but indicates that young adults (aged 45 years or younger) and women were more likely to gain weight and move up at least one BMI category.

The study, by Professor Thomas Yates and Dr. David Kloecker from the Diabetes Research Center, Leicester General Hospital, University of Leicester, UK and colleagues, included information on a UK sample of approximately a million adults mostly from England.

"The implications of even modest weight gain at a population level in younger adults and women could translate into more diabetes, heart disease, cancers and other serious obesity-related health problems over the coming decades in these populations unless action is taken to reverse the effects of lockdown", says Professor Yates. "These data also suggest societal inequalities, with Black individuals more likely to put on pandemic weight and move up at least one BMI category compared to other ethnic groups."

Even before the pandemic, obesity was one of the UK's most pressing public health challenges. According to the Health Survey for England, around three-quarters of those aged 45 to 74 years were living with overweight or obesity in 2019.

For this study, researchers conducted a retrospective observational cohort study of one million adults (aged 18 or older), randomly selected from the Clinical Practice Research Datalink (CPRD—a large general practice database) to investigate how BMI and weight changed after the first COVID-19 lockdown in the UK, and whether these changes differed by BMI category, sex, age group and ethnicity.

The pre-lockdown period spanned 22 March, 2017 to 22 March, 2020 (the day before the start of the first lockdown in the UK), and the follow-up lockdown period was from 23 March, 2020 to 13 March, 2021.

In total, 938,150 adults were included in the first analysis comparing body weight trajectories after the lockdown with historical trends. Participants were divided into five groups based on their first recorded BMI measurement prior to lockdown (between 20 March, 2015 and 22 March, 2020)—32% were classed as underweight (BMI of less than 18.5 kg/m²) or healthy weight (BMI 18.5 to less than 25 kg/m² ), 35% overweight (BMI 25 to less than 30 kg/m² ) and 33% with obesity (either class 1 [30 to < 35 kg/m² ], class 2 [35 to < 40 kg/m² ] or class 3 [≥ 40 kg/m² ]).

Analyses were conducted for the total cohort and stratified by demographic characteristics: sex (male and female), age (under 45 years old, 45 years to <60 years, 60 to <75 years, and 75 years and older), and ethnicity (White, South Asian, Black, and Mixed/Other). The majority (58%) were female and White (83%), with an average (median) age of 55 years.

The researchers found small changes in body weight trends after the start of lockdown in women and those younger than 45 years old with a BMI of ≥ 30 kg/m² relative to historical trends.

Further analyses of data from 273,529 participants (with information on BMI before and after the start of the first UK lockdown) looking at changes in BMI, found that most adults remained in the same BMI category post-lockdown.

In those who started off at a healthy weight (18.5 to <25 kg/m²) before the pandemic, 83% remained in the same BMI category post-lockdown, 14% became overweight or obese, and around 3% transitioned into the underweight category.

Similar proportions of adults living with overweight prior to lockdown experienced weight gain (11%) and weight loss (12%) that led to changes in BMI category post-lockdown. Among adults living with any class of obesity before the first lockdown, around 1 in 10 lost enough weight to transition into the overweight, normal weight or underweight categories.

The researchers also found that a greater proportion of women than men gained weight, resulting in an increase in BMI category post-lockdown. For example, in the overweight category, 13% of women versus 9% of men transitioned into the obesity categories (any class) post-lockdown.

Similarly, compared with older age groups, those aged younger than 45 years were more likely to gain weight and move up at least one BMI category post-lockdown. For example, 17% of adults younger than 45-years old living with overweight pre-lockdown moved into the obesity categories post-lockdown compared with 7%–13% of individuals in the other age groups.

Overall patterns of weight change were similar across all ethnic groups. However, a greater proportion of Black individuals moved up at least one BMI category compared to other ethnic groups, regardless of initial BMI category.

"Prolonged periods of lockdown disrupted daily routines making it challenging for people to eat healthily and keep fit, with emotional eating and sports club closures likely intensifying the trend", says Dr. Kloecker. "Nevertheless, more research is needed to understand the reasons behind these changes in bodyweight and obesity levels.