Salt and obesity

Introduction

Obesity is an increasing problem in the UK. Currently two thirds of British adults are overweight or obese and is predicted to reach 70% by 2034 if current trends continue. Obesity is defined as a Body Mass Index over 30. Male obesity in the UK has increased from 13.2% in 1993 to 26.9% in 2015 while obesity amongst women has increased from 16.4% to 26.8% over the same period (1). Obesity amongst children is also a problem, increasing from 10.9% in 1995 to 15% in 2005 amongst boys aged 2-15. Amongst girls of the same age group obesity has increased from 12.0% to 13% (1). The prevalence of childhood obesity in England increased between 1995 and 2005, but has since remained relatively stable, fluctuating between 14 and 17% since 2008. 

Obesity is huge health burden and is associated with many health conditions. These include diabetes, hypertension, cardiovascular disease, sleep apnea and shortness of breath. In 2002, the direct cost of treating obesity was between 45.8 and £49.0 million pounds and the indirect cost (treating consequences) was around 1 billion pounds (1). The direct cost to the NHS in 2014-2015 was estimated at £6.1 billion per year. The costs attributable to overweight and obesity are projected to reach £9.7 billion by 2050 (1). 

Who is at risk of obesity?

Everyone is at risk of obesity if they consume an unhealthy diet or have an unhealthy lifestyle. However, those most at risk include ex-smokers, people of black African descent, inactive individuals and children (or adults) who also have a high intake of sugared-soft drinks (1). 

How does salt contribute?

Whilst salt is not a direct cause of obesity it is a major influencing factor through its effect on soft drink consumption.  Salt makes you thirsty and increases the amount of fluid you drink. 31% of the fluid drunk by 4-18 year olds is sugary soft drinks2 which have been shown to be related to childhood obesity.(3,4)

It has been estimated that a reduction in salt intake from 10 g/d to the WHO recommended level of 5 g/d would reduce fluid consumption by ≈350 mL/d. A study which analysed the sales of salt and carbonated beverages in the USA between 1985 and 2005 showed a close link between the two, as well as a parallel link with obesity. (5)

An analysis of the NDNS for young people (4 – 18years) showed salt intake was associated with both fluid intake and sugar-sweetened soft drink consumption.(2) A reduction in salt intake by 1 g/d was found to be associated with a difference of 100g/day in total fluid and 27 g/d in sugar-sweetened soft drinks. This demonstrates that salt intake is an important determinant of total fluid and sugary soft drink consumption in children. Reducing salt intake could therefore be important in reversing the current trend of increasing childhood obesity.

In 2015, new research emerged to suggest that salt intake may directly increase the risk of obesity, independent of energy intake or sugar-sweetened beverage intake. The paper, published in the journal Hypertension, analysed data from a nationally representative sample of 458 children and 785 adults participating in the UK National Diet and Nutrition Survey (NDNS) rolling programme, and found that a 1g/day increase in salt intake was associated with an increased risk of being overweight or obese by 26% in adults and 28% in children. The results showed a consistent significant association between salt intake and BMI, waist circumference and body fat mass independent of total energy intake and sugar-sweetened beverage consumption (7). Although the precise mechanisms are still unclear, these findings suggest that reducing salt intake could be beneficial in terms of directly lowering obesity risk. 

Figure 1- Relationship between salt intake and fluid consumption in children and adolescents. Source: He et al, 2008 (2)

Current Salt Intake and Dietary Advice

Almost everyone in the UK (and the rest of the Western world) eats too much salt. The daily recommended amount is no more than 6 grams a day; the current average salt intake is 8.1g a day although many people are eating more than this.

People with or considered at risk of obesity should ensure that they keep their salt intake below the recommended maximum of 6g. This can be achieved by simple changes, such as consuming less processed foods and checking product labels before purchase. Click here for a handy shopping guide to help you identify foods high in salt and the low salt options. 

To further reduce your risk of obesity you should make sure you eat at least 5 portions of fruit/vegetables per day, increase the amount of exercise you do (at least 30 minutes, 5 times a week) and reduce the amount of saturated fat, fat, sugar and calories that you eat. You can use the free FoodSwitch UK app to help you find healthier choices when you shop. It has different filters and shows you similar but healthier choices lower in salt, saturated fat, sugar and calories.

 

References

1. Public Health England, 2017.  https://www.gov.uk/government/publications/health-matters-obesity-and-the-food-environment/health-matters-obesity-and-the-food-environment--2#scale-of-the-obesity-problem
2. He FJ et al. Salt Intake Is Related to Soft Drink Consumption in Children and Adolescents: A Link to Obesity?  Hypertension. 2008; 51, 629-634
3. Ludwig DS et al. Relation Between Consumption of Sugar-sweetened Drinks and Childhood Obesity: a prospective, observational analysis. Lancet. 2001; 357, 505-508,
4. James J et al.  Preventing Childhood Obesity by Reducing Consumption of Carbonated Drinks: Cluster Randomised Controlled Trial. British Medical Journal. 2004; 328,1237
5. Karppanen H, Mervaala E: Sodium Intake and Hypertension. Prog Cardiovasc Dis. 2006; 49, 59-75
6. Hoffman IS & Cubeddu LX. Salt and the Metabolic Syndrome. Nutr Metab Cardiovasc Dis. 2009; 19(2), 123-12
7 Ma Y, He FJ & MacGregor GA. High Salt Intake Independent Risk Factor for Obesity? Hypertension 2015; 66: 00-00