A good (‘healthy’) diet is essential for good health. Conversely, a poor (‘unhealthy’) diet can have lasting detrimental health impacts (see definitions used in this section).

Diet is now the leading behavioural risk factor for illness and death in England. 1 An unhealthy diet can lead to undernutrition, faltering growth in children, tooth decay, overweight and obesity, cardiovascular disease (CVD), type 2 diabetes and some (30% of) cancers.  A healthy diet, on the other hand, promotes both physical and mental wellbeing in a number of ways (see definitions ). 2 3 4 5

Figure 1: The positive and negative impacts of diet

Healthy diet encourages less illness, positive wellbeing, longer life, healthy weight and better growth, repair and immunity
Figure 1: The positive and negative impacts of diet

Source: City & Hackney Public Health Team

UK government recommendations for a healthy diet are set out in the Eatwell Guide, presented in Figure 2. Despite these guidelines, many people do not achieve a healthy diet as described in the guide. For example, the majority of the adult and child population in England do not eat enough fruit and vegetables, fibre or oily fish; but consume too much salt, sugar and saturated fat. 6 7 8

Specifically in relation to sugar, there is growing evidence that free sugars and sugar-containing drinks are an independent risk factor for weight gain and type 2 diabetes. The UK Scientific Advisory Committee on Nutrition (SACN) recently reviewed the evidence, which resulted in a change to the dietary guidelines for sugars – reducing the recommended level from 10% to 5% of total daily energy intake. 9  All population groups in the UK now exceed this revised guideline level of consumption. 10 Public Health England (PHE) have estimated that almost 250,000 cases of tooth decay could be avoided each year if the SACN target was achieved over the next five years. 11

Figure 2: The Eatwell Guide

Figure 2: The Eatwell Guide

Source: Public Health England in association with the Welsh Government, Food Standards Scotland and the Food Standards Agency in Northern Ireland (2016).


  1. J. N. Newton, A. D. Briggs, C. J. Murray, D. Dicker and K. J. Foreman, “Changes in health in England, with analysis by English regions and areas of deprivation, 1990-2013: a systematic analysis for the Global Burden of Disease study 2013,” The Lancet, vol. 386, no. 10010, pp. 2257-2274, 2015.
  2. Report of the joint WHO/FAO expert consultation , “Diet, nutrition and the prevention of chronic diseases,” World Health Organisation, London, 2002.
  3. World Cancer Research Fund, “Food, Nutrition, Physical Activity and the Prevention of Cancer,” World Cancer Research Fund / American Institute for Cancer Research, Washington , 2007.
  4. The Mental Health Foundation , “Feeding Minds. The impact of food on mental health,” The Mental Health Foundation , London, 2006.
  5. A. I. Conklin, P. Monsivais, K. Khaw, N. J. Wareham and N. G. Forouhi, “Dietary diversity, diet cost and incidence of type 2 diabetes in the United Kingdon: A prospective cohort study,” PLOS medicine, vol. 13, no. 8, 2016.
  6. Public Health England, “National Diet and Nutrtion Survey (NDNS),” Crown Copyright, Lonon, 2014.
  7. Public Health England, “Adult Diet Data factsheeet,” ONS, London, 2016.
  8. Public Health England and the Food Standards Agency , “National Diet and Nutrition Survey. Results from Years 5-6 (combined) of the Rolling Programme (2012/13-2013/14),” Crown Copyright , London , 2016.
  9. SACN, “Carbohydrates and Health,” TSO, London, 2015.
  10. Public Health England, “Adult Diet Data factsheeet,” ONS, London, 2016.
  11. Public Health England, “Sugar Reduction: from evidence to action,” Crown, London, 2015.