In the worldwide war against obesity, we’re constantly being told that our waistlines too wide.
According to the Australian Institute of Health and Welfare, almost two in every three Australian adults were overweight or obese in 2014/15. The statistic is shared in other parts of the Western world with two-thirds of Britain also being overweight.
As a result, we Westerners are regularly advised by health professionals to cook more meals at home and avoid buying highly processed foods, like frozen pre-packaged meals available in the supermarket.
What we’re not always told is why – why, exactly, are frozen meals that are low in calories so damaging to our weight loss goals. Why is a hypothetical lean frozen meal – let’s say a chicken and vegetable stir-fry – worse for weight gain than the exact same meal cooked at home in an equal proportion using identical ingredients?
Dr Giles Yeo, principal research associate at the Institute of Metabolic Science with Cambridge University offers scientific reasons in episode one of the new SBS series, Hugh’s Fat Fight, premiering on Monday 17 September, at 8.30pm.
Dr Yeo explains something called ‘caloric availability’ – a rationale, which infers that not all calories are processed by our bodies equally.
As Dr Yeo tells the show’s host, English celebrity chef Hugh Fearnley-Whittingstall, caloric availability refers to the amount of “calories you can get out of the food, as opposed to how many calories are in the food”.
“It’s not the same number,” Dr Yeo explains to Hugh’s shock.
Calorific availability infers that the net calorific count present on food labels on the processed meals we consume does not reveal all the information we need to know to weigh up the nutritional value of one meal versus another.
“It takes energy to extract calories out of food: not only do you have to chew, you have to digest then chemically you have to break the various energy bonds in order to release energy."
Dr Yeo suggests that net caloric counts on food labels may not take into account how much energy we use to digest a particular meal or how our oral and gut bacteria processes the calories we eat. It also ignores how fast a particular food passes through our intestines and whether or not the food is resistant to digestion.
“It takes energy to extract calories out of food: not only do you have to chew, you have to digest then chemically you have to break the various energy bonds in order to release energy,” says Dr Yeo.
“But if a lot of the work has been done for you by the processing [of a frozen meal], you’re going to get more calories out of the 400 calories of a ready meal than the 400 calories [of a meal] you cooked yourself at home.”
So although frozen meals are convenient and may claim to be lean, the same version cooked and eaten at home may be better for your waistline.
Many scientists and obesity experts also believe that not all calories are equal to each other. For example, 300 calories contained in a fresh vegetable is not the same as the 300 calories in a packet of chips or a chocolate bar.
“When [a meal is] highly processed, you remove flavour which means you have to add more fat, and more sugar and more salt in order to make it more tasty."
A 2015 study published in the International Journal of Obesity discusses how past observational and randomised controlled studies have shown that calories from sugar-rich soft drinks, refined high high glycemic index (HGI) carbohydrates, and energy-dense fat-rich fast foods can make you put on weight and become obese. These foods can also drive up caloric content because they do not fill you up.
Meanwhile, the calories from diet-sodas, whole grain and low glycemic index (LGI) carbohydrates may decrease risk of weight gain and obesity.
In episode one of Hugh’s Fat Fight, Dr Yeo also reminds consumers that calories only tell one part of a meal’s nutritional story. Fat content and sugars are also important inclusions that you need to pay attention to when assessing the nutritional content of a meal.
“When [a meal is] highly processed, you remove flavour which means you have to add more fat, and more sugar and more salt in order to make it more tasty,” says Dr Yeo.
The new three-part series, Hugh's Fat Fight, starts on SBS on Monday 17 September at 8.30pm and will air on Mondays at the same time thereafter. Episodes will be available to stream on SBS On Demand after broadcast.
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