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Prof Peter Rogers: Don't tell me you're hungry; it's just your excuse for eating too much.

5 April 2016

The provocative title clearly stirred up interest resulting in a large turnout. Professor Peter Rogers gave a humurous talk that challenged a range of common beliefs about eating. Hunger is a word that is used a lot in the literature, but rarely defined. It is implied that hunger is caused by energy depletion and the need to replace energy we use. Homeostatic hunger is considered as the 'normal' and 'healthy' way of eating in contrast with the hedonic hunger which is driven by pleasure and often considered as maladaptive and dysfunctional. It is suggested hedonic hunger can override homeostatic hunger, and the temptation arising from easy access to low cost and delicious food is linked to overeating and obesity. 

However, is it really possible to distinguish between eating to replenish energy and eating for pleasure? Perhaps not. For example, if you expend 500 calories then consume a 1000 calorie meal would that mean that the first 500 calories were driven by homeostatic hunger and the last 500 are consumed for pleasure?

Eating due to energy depletion from meal to meal is not logical consdering that a well-nourished person has 75 days' worth of energy stored in their body (Frayn, 2010) therefore, the amount of energy in a single meal is trivial in comparison. This is supported by observing that glucose levels remain fairly constant irrespective of when we last ate. Pollitt et al., (1981) found when children skipped breakfast they performed significantly better on a range of cognitive tasks compared to when they ate breakfast with the exception of sub-group of children with below average IQs. Addtionally, Rogerst et al. (2013) found consuming a big breakfast was linked to slower reaction times and memory impairments in comparison to no breakfast. 

Peter presented his saucepan and bathtub model of eating. Food goes into the stomach and intestines (saucepan) and stored in the body (bathtub). Body energy stores (bathtub) are replenished from the gut (saucepan). Both the gut and the body fat stores resist being filled proportionally to their contents sending negative feedback to the brain. Digesting food is a physiological challenge for the body, blood pressure rises to increase bloody flow to the gut and, therefore, feeling sleepy is an adaptive response to reduce movement while the heart is working harder (Bazar, Yun & Lee). Eating inhibits hunger quickly as the saucepan is easily filled, whilst the amount of energy expended during exercise is trivial in comparison to the capacity of the bathtub.

Eating is also motivated by pleasure, energy dense foods with lots of calories per gram, for example, chocolate are more rewarding than energy diluted foods, for example, boiled potatoes because they are less filling per calorie. Biologically we eat to gain nutrients, rather than to become full. 

If one wants to eat less, a simple solution is to miss a meal. Levitsky (2005) found people that missed a 625 calorie breakfast only consumed an additional 135 calories at lunch and total daily intake was reduced by 495 calories. This result is surprising, and goes against NHS recommendations to eat breakfast even if you are not hungry. There is strong evidence associating missing breakfast with being overweight, however, as the data is correlational it is wrong to assume that missing breakfast itself causes obesity. In fact, fasting for a day is an effective way of reducing energy intake, and does not affect food consumption on the days that follow (Levitsky, 2005). In conclusion, believing that missing breakfast causes obesity, make us eat more and impairs cognitive functioning  is extremely unhelpful for maintaining a healthy weight. Along with more general ideas that hunger is driven by energy depletion and notions of food addiction deter us from eating less. The talk was both thoroughly entertaining and thought-provoking. The following day I skipped breakfast, and enjoyed a chocolate bar mid-morning, feeling smug because now I have references to rationalise these decisions (even if this was a slight misuse of the evidence.

Caroline Thomas


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