Select Committee on Health Minutes of Evidence

Memorandum by Professor Andrew Prentice (OB 74)



  MRC scientist with 20 years experience researching the physiological and environmental factors causing changes in body weight and obesity.


  My evidence will only address bullet point 3 of the Committee's terms of reference:

What are the causes of the rise in obesity in recent decades?

  What has been the role of changes in diet? To what extent have changes in lifestyle, particularly moves to a more sedentary lifestyle, been influential? How much is a lack of physical activity contributing to the problem?

1.  Causes of obesity

  Obesity is a perfectly predictable biological response to the massive change in the external environment caused by the technological/electronic and agricultural revolutions of the late 20th century. Both sides of the energy balance equation have been affected and causality can be attributed with roughly equal measures to sedentariness and the super-abundance of cheap, highly-refined energy-dense foods.

  A corollary of the fact that obesity results from normal physiology doing what nature intended it to do (ie lay down fat in times of plenty) is that we should be very concerned about the widespread use of drugs or surgery to fix the problem. Genetic explanations (eg the "thrifty gene" theory) are interesting, but largely irrelevant to finding a global solution to the epidemic.

2.  The role of inactivity

  In 1995 Prentice & Jebb published a much-cited paper in the BMJ entitled "Obesity in Britain: Gluttony or Sloth?" (see Annex 1). This gathered evidence from a number of epidemiological studies and government statistical sources to examine the relative role of diet and physical inacitvity in the causation of nationwide obesity. The evidence suggested that physical inactivity was a major driver of the change. However, we were very careful in the wording of our conclusions and stated that "Evidence suggests that modern inactive lifestyles are at least as important as diet in the aetiology of obesity and possibly represent the dominant factor". We and others have written extensively about the nature and extent of changes in energy expenditure in recent decades, so this does not need to be rehearsed here. Suffice it to say that inactivity is incontrovertibly a major predisposing factor enocuraging weight gain.

  Our BMJ paper was important in being the first to really draw attention to the "sloth" side of the argument. Unfortunately it has since been wilfully misused by some arms of the food manufacturing and retail industries to assert that physical inactivity is the only cause of the problem, and hence to deflect blame from themselves. The edvidence does not support this, we never stated it, and we welcome the public opportunity to refute the contention.

3.  The role of diet

  Clearly the nation is consuming considerably more energy that it requires. This does not necessarily equate to an absolute increase in energy intake, rather to an increase relative to our new lower energy needs caused by sedentary lifestyles (see Annex 2).

  A considerable amount of research by our group and others has demonstrated that the energy density of foods (kcal or kJ per unit weight) is a key determinant of overall energy intake, and that human appetite control is readily undermined by very energy-dense foods (see Annexes 2 and 3). We believe that a focus on reducing the energy density of modern diets will be helpful in combating obesity trends. An advantage of concentrating on energy density is that it side-steps the currently polarised views about the relative impact of carbohydrates and fats. It should be noted that energy density needs to be viewed differently for liquid and solid foods due to the lower satiating value of liquids. Sugars contribute greatly to the energy-density of soft drinks, whilst both fat and refined sugars contribute to the energy density of solid foods.

  Certain food outlets, notably "fast food" restaurants, have menus which are almost universally composed of very energy-dense foods (see Annex 3). We believe that these put regular consumers at particular risk. The risk is exacerbated by marketing techniques designed to encourage the consumption of larger portion sizes.

  In general, the recent changes in the British diet (ie larger portions of energy-dense foods consumed with greater frequency) are diametrically opposed to what would constitute the logical response to the reduction in our energy needs caused by technolgoical change. Manufacturers and retailers need to be made more aware of this paradox, and brought on board to assist with engineeering a more rational dietary environment.

  Like the tobacco industry, companies with products now deemed to be causing a health hazard (eg soft drink manufacturers, fast food outlets) did not set out to create unhealthy products. However, now that the consequences of high levels of consumption are clear, it is reasonable to hold them morally responsible for amending their products and marketing practices. In the absence of firm government action vested interests in the food industry will demand absolute proof about the involvement of their particular products in causing obesity before agreeing to change. We will face a re-run of the tobacco denial story. In my (rather limited) experience of discussions with some of the key players in the field, most companies would be likely to comply with voluntary agreements or legislation so long as they have a level playing field on which to compete (see Recommendations 4, 5).

Recommendation 1

  The debate about whether diet or activity is primarily responsible for the obesity epidemic is unhelpful. Both are critical, and both should be the subject of government-led multi-sector initiatives. Propagation of the debate allows certain sectors of the food industry to exploit the perceived controversy as a diversionary tactic. The Health Committee should accept and promote the fact that both sides of the energy balance equation are critical—probably in about equal measure.

Recommendation 2

  Encourage any and all possible means to increase public awareness about the damaging health consequences of inactivity. We need people to appreciate that inactivity is a major risk factor for ill health. The CMO's forthcoming report will be an important step in this direction and should be translated into simple media messages for widespread propagation.

  Focus interventions towards increasing children's and young people's enjoyment of active pastimes and sports. Policies aimed at young adults are also important, since this is when many people abandon sports and activities. Consider the advantages of extending the school day by staggering the employment hours of academic and physical education staff so that time can be created for sports and active leisure training within the formal curriculum.

  I strongly endorse the many suggestions made by others concerning changes to the urban and architectural environment, and to transport policy, which will foster more active lifestyles. Since these have been dealt with in detail by others I will not expand on them here.

Recommendation 3

  Educate the public about the importance of energy density in regulating an approriate energy balance. Note that existing (and the proposed stronger) food labelling laws already list energy per 100g and per portion.

  An advantage of this approach is that it will inhibit manufacturers from replacing fat by other energy-dense ingredients (usually highly-refined carbohydrates and sugar). It also gets around the fat versus carbohydates controversy).

Recommendation 4

  Legislate to enforce labelling with fat, added sugar, energy and salt content of foods and meals. Meals should be listed per serving. In fast food outlets the listing should be prominently displayed and printed on the meal packaging.

  Consider adopting a similar labelling system to the US where recommended "Daily Amounts" for men and women are listed on the labelling panel in order to give the consumer a point of reference. Fats, energy, salt and sugar might profitably be listed as a percentage of the DA.

Recommendation 5

  Seek voluntary agreements from industry (or legislate if necessary) to outlaw marketing practices based on "supersizing".

  In this respect, outlaw the pricing of products such that larger sizes are relatively cheaper. This could be applied only to certain foods categories such as soft drinks, confection and fast foods.

Recommendation 6

  Urgently consider measures to control the advertising of "unhealthy" drinks, snacks and foods to children.

July 2003

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