How food tax policies can lower the risk of Type 2 Diabetes
Diabetes prevention programs are an effective individual-level approach to prevent type 2 diabetes in those at high-risk. Dr Nicola Guess, Division of Diabetes and Nutritional Sciences at King’s College London, says food taxation policies are needed to prevent type 2 diabetes at a macro level
The current epidemic of prediabetes and type 2 diabetes (T2D) is largely driven by overweight and obesity. The prevalence of T2D in people at a normal weight is 2%, rising to 13% in those who are obese. Each additional 1 kg increase in body weight increases a person’s risk of T2D by 4.5-9%. It is also clear that losing 5-7% of body weight can reduce the risk of developing T2D in people with prediabetes.
While a common view on weight gain is that it is a result of will-power and poor choices, in reality the causes of weight gain are multifactorial and complex. Consider school-children leaving a class on nutrition only to find 3 or 4 fast-food outlets on the high street, where 850 kcal can cost only £1.85. Or where instead of unprocessed, high-fibre cereals which are known to send satiety signals to the brain, a supermarket shelf primarily consists of highly-processed foods, which, rather than promote satiety, may override the body’s natural appetite feedback mechanisms.
More critically, once a person is overweight, a variety of physiological feedback mechanisms combine to drive that person towards weight regain. New evidence suggests that in addition to an increase in hormones which promote hunger, weight loss also causes the body’s metabolic rate to reduce, and these unfortunate changes in appetite and metabolism remain altered up to 7 years after a person loses weight.
Such responses to weight loss are likely a remnant of our hunter-gatherer genetics, formed during thousands of years where food was scarce, and during a time where losing weight easily would have resulted in the extinction of our species. Reducing overweight and obesity in an already overweight and obese population is therefore not a feasible proposition.
Put it in this context, the challenge to reduce T2D in our populations is immense. A two-pronged approach is needed by which 1) T2D is prevented or delayed in people who are already at high-risk of T2D and 2) obesity is prevented by combined taxation and educational policies.
The first approach is exemplified by the NHS Diabetes Prevention Programme in the UK. This programme is an implementation of the irrefutable evidence that moderate weight loss following a lifestyle programme prevents T2D by up to two-thirds. Importantly, even 10 years after these programmes finish, participants’ risk of T2D is still reduced even if they regain the weight.
However, these programmes are expensive and labour-intensive. There are currently an estimated 6 million people in the UK with prediabetes. Unless the obesity crisis is addressed, this number may rise to 8-10 million by 2025. Therefore, while the NHS Diabetes Prevention Programme will help prevent T2D in people already at-risk, we must prevent as many people as possible from becoming high-risk in the first place. This will require preventing obesity by changes in tax policy and education at the macro-level.
A “sugar-tax” implemented in Mexico on January 1st 2014 reduced the average consumption of sugar-sweetened beverages by up to 17% by the end of the year, while consumption of plain bottled water increased by 4%. In a small study in a school cafeteria, halving the price of fruit and salad tripled their consumption. When the cafeteria re-introduced the original price of fruit and salad, consumption reduced again.
Similarly, halving the price of low-fat items in a vending machine increased their consumption by 93%. However, here is an example where tax policies need to be coherent, and where nutrition education can maximise success: Low-fat cereal bars may be sweetened with sugar and contain an abundance of refined starch. By taxing high-sugar and high-fat products together, a person is “nudged” to make a truly healthier choice. Secondly, someone who has received education on nutrition in school is equipped to recognise a truly healthy choice.
Educational policies aimed at children and their families appear to be the most effective approach at changing dietary and exercise habits. In a study in Greece, a one-year educational programme increased the consumption of fruits, lowered the consumption of fats, oils, sweets and sugary drinks and reduced body weight and blood pressure after one year. While long-term evaluation of similar programmes shows that people revert to unhealthier habits over time, with food taxation policies which support healthy dietary changes, their long-term effectiveness can be optimised.
In summary, T2D can be prevented in individuals with prediabetes by lifestyle programmes to improve diet and exercise habits. Changes in food taxation policy are urgently needed to support these healthy dietary habits long-term. More importantly, such changes in the food landscape are needed to halt the obesity crisis which is driving the T2D epidemic