Intended for healthcare professionals

Opinion Dissecting Health

Scarlett McNally: Obesity is a community issue, not just an individual one

BMJ 2023; 380 doi: (Published 29 March 2023) Cite this as: BMJ 2023;380:p702
  1. Scarlett McNally, professor
  1. Eastbourne
  1. scarlettmcnally{at}
    Follow Scarlett on Twitter @scarlettmcnally

In the 30-odd years since I qualified, England has had 14 obesity strategies including 689 policies.1 In that time the prevalence of obesity has almost doubled, from 15% in 1993 to 28% of UK adults with obesity in 2019.2 This spectacular failure of policy is probably due to a misplaced focus on individual behaviours rather than social, fiscal, or regulatory policies.

High body mass index is the fourth leading risk factor for disease in the UK3 and a major risk factor for 13 cancers.4 The top causes of ill health are those related to dietary factors, physical inactivity, smoking, and pollution.3 People with obesity are seven times more likely5 to develop type 2 diabetes due to insulin resistance, contributing to worsening health and the risk of amputations, sight loss, kidney dysfunction, and complications of surgery.

Several key aspects of physiology are not widely understood or applied. Firstly, complex carbohydrates (bread, pasta, rice, and potatoes) are rapidly converted to sugars that are preferentially stored as fat. Release of the hormone insulin is triggered by high sugar levels, helping to store sugar as fat and leading to the “post-prandial dip” in blood sugar level around two hours later, which stimulates hunger and more food consumption. Fats, proteins, and fibre cause a lower insulin spike, leaving us feeling fuller for longer. This is the basis of low carbohydrate diets.

Secondly, the balance of hormones means that our bodies are either storing fat or using it. There’s a binary switch in the suite of hormones: any food intake reduces fat loss for some time. This is the justification behind “intermittent fasting” regimens.

Thirdly, it takes 20 minutes to feel full: slower eating helps us to plan portion sizes and second helpings. And fourthly, exercise encourages the body to burn fat by lipolysis.6

So, what do we do with this knowledge? Perhaps suggesting what and when to eat is a better option than new, expensively promoted semaglutide injections, which mimic a hormone that decreases appetite.7

Nutrition and exercise

It seems outdated that Public Health England’s advice still exists as an “eatwell plate” with 38-50% of its calories from carbohydrates,8 when many people’s carbohydrate intake is driving their obesity. The Scientific Advisory Committee on Nutrition already recommends low carbohydrate diets for people with type 2 diabetes.9 And real world studies of people with type 2 diabetes show that a low carbohydrate diet and moderate exercise cause significant reductions in obesity, improved blood lipid profiles, lowering of blood glycosylated haemoglobin, and higher drug-free remission rates.1011

Exercise must be added to any attempt to improve nutrition.12 The EAT-Lancet report recommends less processed food, less carbohydrate (especially types with a high glycaemic load that raise blood sugar rapidly), and more unsaturated fat to ensure healthy and sustainable diets.13

Replacing carbohydrates means that more protein, fat, or fibre is needed. This can be difficult in a cost of living crisis, as obesity is highly related to social deprivation. A person is twice as likely to experience obesity (37%) in the most deprived areas as in the least deprived (19%).14 Tackling obesity, then, should include social initiatives to fight deprivation, such as healthy free school meals.

Our environment needs to change, through improved funding and regulation, to reduce obesogenic environments. The physical environment should permit physical activity, with play parks, walkable neighbourhoods, cycle lanes, and low traffic areas. Commercial food companies should be subject to the full weight of regulations, which should be applied to any junk food advertising to reduce consumption of unhealthy foods.1 We need initiatives to improve access to affordable, high quality food, which is shamefully poor in many deprived areas.

Obesity should no longer be considered an individual “lifestyle” problem—it requires a whole community approach focused on environments, regulation, and funding.


  • Competing interests: Scarlett McNally is a consultant orthopaedic surgeon. She won a prize in physiology in 1988.

  • Provenance and peer review: commissioned, not externally peer reviewed.