"Eat to Live, Not Live to Eat"
John H Weisburger, 2000
The current obesity epidemic is due to changes in society - modernisation results in over-nutrition and a sedentary lifestyle. The phenomenon largely began in the developed world only a few decades ago and has rapidly become global. Australia is no exception, with almost two thirds of adults being either overweight or obese (body mass index, BMI>25). The situation is serious as high BMI is at the core of so many degenerative and chronic diseases, and people are generally aware that something needs changing to minimise dramatic loss in quality and longevity of life, economic productivity and over-whelming individual and societal costs. Long term dietary changes are one arm of a preventative strategy that can address the problem. But losing weight and keeping it off once gained is very hard for almost everyone, and many resort repeatedly to the latest fad diet. only to find it doesn't amount to real gains. Despite endless discussion about the impact of genes, family and traditional habits, psychology etc, putting on weight comes down to an imbalance between energy intake and expenditure. All these driving factors may be involved. but if the imbalance has developed, what can be done about it?
Amongst all the knowing advice out there about how to minimise energy intake, how many times have you been told in TV documentaries, health magazines, newspapers, web articles etc that drinking a glass of water or other low-calorie drink before a meal will fill part of the stomach. so that when food is subsequently eaten, the full feeling will be experienced earlier, resulting in fewer total calories consumed? Well, the following recent US study (Appetite (2009), 52, 416–422) investigated this perceived 'wisdom' with different fruit products and found it to be false. It's common practice for many people to consume a glass of (say) orange juice either before or during their breakfast or other meals. The healthy nutritional benefit from this practice is a separate issue to the weight control focus here, and as these considerations have been discussed elsewhere in this series (see More Fruit, Less Juice and others) they won't be discussed further.
Consuming whole fruit reduces ratings of satiety more than fruit juice, but little is known about the effects of different forms of fruit on subsequent energy intake. This study tested how consuming pre-loads of apples in different forms prior to a meal (fresh apple, cooked applesauce, and apple juice with and without added fibre) influences satiety and energy intake in the subsequent meal. Pre-loads were matched for weight, energy content, energy density, and ingestion rate. Once a week for 5 weeks, 58 adults consumed one of four pre-loads (266g each, 125kcal) or no pre-load taken as the control, followed by a test meal consumed ad libitum 15 min later. Results showed that eating apple significantly reduced total energy intake (pre-load + test) compared to control (837 cf 1024kcal resp), with a reduction of 18%. Applesauce also had a significant but reduced effect (928kcal) but neither of the juices had any significant effect. Fullness ratings differed significantly after pre-load consumption with apple > applesauce > both juices > control. Overall, whole apple increased satiety more than applesauce or apple juice. Adding naturally occurring levels of apple fibre to juice did not enhance satiety. These results suggest that solid fruit affects satiety more than pureed fruit (applesauce) or juice, and that eating fruit at the start of a meal can reduce energy intake.
The interval between pre-load and main meal intake has significant effects on this phenomenon – the longer the interval the less effect. The present authors chose an interval of 15 min as being representative of the time between a typical entrée and the subsequent meal, for example between courses served in restaurants. Subjects were instructed to consume the pre-load in 10min and then after a further 5min to have the ad libitum test meal. To avoid social interactions and their effects on eating behaviour all participants ate the test meal isolated from one another. Fruit juices are very popular products, both commercially-supplied and home-made. Unless a puree is made with all fruit components being present, juices are invariably strained to remove off-colours, tastes and solid matter associated with skin, fibre and seeds. In the present study the authors tailored their pre-loads to reflect these background habits. For most meals, no pre-load is eaten so they took this as the control. The fruit juices were strained (skin and fibrous material removed). Because fibre has been shown to influence satiety, they then added apple pectin (soluble fibre to give the same fibre concentration as in whole apple) to a second juice pre-load. The applesauce was skinned apple cooked then pureed, and the whole apple with skin removed was served in pieces. As stated above, these four pre-loads were then matched for weight, energy content, energy density and ingestion rate (10min). There were a number of exclusion criteria from the trial such as people who had abnormal energy balance reflected in unhealthy BMI (<18 and >40), standard questionnaires were used to exclude any with symptoms of depression, those who were currently engaged in weight loss diets. taking significant medications etc. Each subject in a cross-over clinical trial acts as their own control, so minimising variability between people.
Other studies with apples, oranges and grapes on the greater effect of solid foods on satiety suggest that it's due to the longer times that food stays in the mouth while chewing and salivating that generates stronger hormonal/sensory feedback to the brain compared to more liquid forms which are quickly swallowed. A more general finding in this direction is that slower eating gives time for these hormonal messages to build up resulting in a feeling of fullness. Eating quickly often means you consume more than necessary before the internal 'finished/full' signal gets thru; the outcome if habitually maintained predisposes to weight gain. Of course an extra benefit with slower eating is that you have an increased chance to savour and enjoy what's being consumed.
Another facet of this story is the irregular and increased frequency of food intake associated with Westernised lifestyles, supported by the widespread availability of fast food outlets selling cheap, calorie-dense foods, highly-sugared drinks and treats, ready-prepared supermarket offerings, habitual snacking, skipping meals and generally being time-poor. For many, three regular and filling meals a day is no longer the norm and hunger builds up before the next regular meal. If additional snacks throughout the day are desired or necessary, fruit always represents a better choice than biscuits, cakes or confections. So too is a preference for fruit rather than ice-cream or cheese cake if you have dessert after meals. But the study quoted above suggests if you want to lose weight, then it would help to have fresh fruit or fruit salad as an entrée just before the meal instead of afterwards. If you have three adequate and filling low glycemic index meals a day, clinical trials have shown that fewer daily calories are consumed compared to 6 or 9 smaller meals at irregular intervals. Other studies in Japanese children have shown those who skip meals and eat irregularly are more likely to be obese. In addition to lower daily calorie intake with regular meals, there is an increased thermogenic effect of foods, meaning more carbohydrate and fat is burned (oxidised) than stored as fat in the body.