In this article, Prof Bruce Griffin explains the importance of regular meals and portion size on maintaining your optimum weight. 

Bruce Griffin

Professor of Nutritional Metabolism,

Department of Nutritional Sciences, University of Surrey, U.K.

Obesity can be viewed as an inevitable consequence of human devolution, from early hunter-gatherers into a domesticated species with modern diet and lifestyles that are inappropriate for maintaining a body weight that is optimal for long term health. Hunter-gatherers had to endure an intermittent pattern of feeding, and prolonged periods of fasting that were imposed by a scarcity of food and extended periods of darkness in the absence of artificial light. Their diet would have been unrefined, and their metabolism and energy balance adapted to storing nutrients in body fat and muscle for periods of fasting1. These tissues were also finely tuned for the efficient release of energy to maintain body heat and for endurance activities when hunting prey. Sadly, there are no medical records to tell us about the rates of obesity, diabetes and cardiovascular disease in these primitive humans. However, we do know that hunter-gathering tribesmen and mammals in the wild maintain a body weight that is optimal for health, and do not succumb to these life threatening diseases.

Compare and contrast this primitive lifestyle with modern humans who have ready access to a wide variety of energy-rich foods, containing refined carbohydrates, fats and oils. They seldom have to fast, and have extended opportunities to over consume food under artificial light, well into the night1. Many live in centrally heated homes, are physically inactive and consume a regular pattern of meals throughout the day. While the latter may actually be of some benefit to health by helping to co-ordinate and synchronise the intake of food with the natural rhythms in our metabolism (circadian rhythms), modern lifestyles can disrupt this regular pattern of eating, through mistimed and missed meals2.  These meals may be replaced with energy-dense snacks and the consumption of food late into the evening and night, when our body is preparing to sleep and is unresponsive to food intake. Prolonged exposure to this lifestyle over many years can exert adverse effects on health by disrupting energy balance through increased appetite and hunger, and reduced feelings of fullness (satiety). The over consumption of food energy, results in an increased storage of fat, especially in the abdomen (central obesity). This stored fat can spill-over into internal organs like the liver and pancreas, and into fat tissue and muscles, making these organs and tissues insensitive to the essential actions of hormones like insulin.  One of the main roles of insulin is to extract sugar and fat from the blood after eating, for long term storage in bodily tissues.  Failure of insulin action, a common condition in obesity that is known as insulin resistance, results in raised levels of blood sugar and fat after eating a meal. This can lead to a disruption of metabolism that can contribute to the development of chronic diseases like diabetes, cardiovascular disease and cancer3.

An important question is whether it is possible to reverse these adverse effects on health by adopting the eating habits of a hunter-gatherer? On the strength of the available evidence for the health benefits of intermittent food intake and fasting, the answer is probably ‘yes’.  It is well established that restricting the intake energy from food will eventually result in weight loss. However, in most cases all of the weight that has been lost is eventually regained because the dietary restriction required to achieve the lower body weight cannot be maintained because of poor dietary compliance. In other words, diets actually work in promoting weight loss, but humans don’t!   In comparison to calorie-restricted diets, interventions that include timed-restricted feeding and intermittent fasting, such as the well publicised 5/2 diet, have been shown to be effective in promoting weight loss4,5.  One possible explanation for how they do this is that they achieve greater compliance than a calorie restriction diet alone. Intermittent fasting may also increase the sensitivity of tissues to insulin (reduce insulin resistance), and exert effects on the co-ordination of circadian rhythms associated with energy metabolism that promote weight loss, and are beneficial to cardiovascular health.  Fasting is known to induce a mild metabolic stress that prepares the body for further stress, by suppressing appetite and the desire to eat, and increasing satiety.  The timing of meals (energy loading) throughout the day can also influence body weight. There is evidence to suggest that consuming energy in your main meal earlier as compared to later in the day can facilitate weight loss on a calorie-restricted diet6,7. Interestingly, this finding is in keeping with the pattern of food intake from 50 or 60 years ago, when the main meal of the day was often consumed closer to midday than late in the evening.

The major challenge remains of how to promote and maintain weight loss in populations, in the face of the incorrigible behavioural, social and commercial pressures that make humans over eat.             In addition to conscious efforts to reduce portion size and select healthier food choices, the manipulation of meal timing and intermittent fasting represent useful ways to alter our physiology to reduce the desire to eat, and increase our resilience to an obesogenic environment.



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