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Our obsession with fats and carbs means we’re looking at nutrition all wrong


By Stephen Simpson and David Raubenheimer

A plate with a sad face made out of berries. Photo: We demonise fats, carbs and salt by implying that reducing their intake alone will solve the problem of obesity, but it won’t. (iStockPhoto)
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“Eating pasta helps you lose weight.” “Eating more animal protein increases risk of death.” “The foods helping you shred stomach fat.” “How to eat carbs without gaining weight.”

These are all real headlines, published in separate media articles in the past month.

Is it any wonder that people are confused about what they should and shouldn’t eat?

Daily we hear of another nutritional dietary “breakthrough”. But as a cursory look at Australia’s obesity statistics attests (two in three Australians are obese or overweight), our health and wellbeing are reaping no benefit.

What’s worse, fats or carbs?

So what’s gone wrong? Why are clear, useful and effective messages about nutrition so difficult to find?

The answer is that we have taken a wrong turn in the way that we think about nutrition. We are too obsessed with identifying an individual culprit — a specific nutrient that causes a particular health problem.

Take for example the argument whether fats or carbs causes obesity. It began over half a century ago, and yet the debate remains unresolved.

Some experts argue that fats are to blame, others that carbs (especially sugar) are almost solely to blame, and to further complicate things, yet others suggest too much protein or too little fibre as the cause.

None of these viewpoints is entirely incorrect, but in reality, obesity is not caused by a single nutrient.

Rather, like a high-functioning sports team, particular nutrients interact in networks of other nutrients to influence energy intake and fat storage.

To solve the problem we need to reconsider the question we ask. Rather than “which nutrient causes obesity?”, we should ask “which combinations of nutrients are associated with obesity?”

Nutrition is about mixtures, not single nutrients, and their actions can be indirect and unexpected.

We had bad dietary advice in the ’70s

Not only has the single-nutrient approach failed to manage the obesity crisis, it might actually have contributed to it. In the 1960s and 1970s, when obesity first emerged as a serious health problem, dietary fat took too much of the rap.

Official advice was, quite logically, to reduce the amounts of fat in the diet. And we did — the public health messages worked, but it had no effect. By the 1980s it was clear there was no sign of the obesity epidemic slowing, let alone reversing.

People followed the dietary advice, but it was bad advice. It failed not because fats aren’t associated with obesity — they probably are — but because the focus on a single nutrient had unintended consequences.

Rather than reduce the total amount of energy eaten, which very likely would reduce obesity, people simply replaced fat in their diet with carbs.

Paleo Pete by Tim Storrier Photo: This Tim Storrier work lampoons celebrity chef Pete Evans, a proponent of the so-called paleo diet. (Tim Storrier)

This was also helped, in no small measure, by the processed foods industries. Sensing an opportunity, they quickly offered foods conspicuously labelled “low-fat”. What the labels didn’t say is that these foods were also “high-carb”.

Paleo and Banting diets have issues

So if fat isn’t responsible, and obesity has continued to rise with increased carb intake, then surely carbs must be to blame.

Excessive carb intake almost certainly has played a role in the obesity epidemic (probably together with fat), but there are again suggestions that singling them out as “the cause” is leading to problems.

It is causing many to turn to a low-carb diet — for example the paleo, Atkins and Banting diets. But recalling the fat-carb debacle, if carbs are reduced then it is likely that something else will replace them. That something turns out to be protein.

Although low-carb/high-protein diets likely do lead to reduced energy intake, the evidence is growing that they also have nasty side-effects. They alter the balance of microbes in the gut, accelerate the onset of age-related diseases such as cancers, and shorten lifespan.

Demonising fats, carbs, salt, or zangamide (we just made that up), and implying that reducing their intake alone will solve the problem of obesity, is simply wrong. That’s because attempting to solve health problems nutrient-by-nutrient is like herding cats. As soon as one nutrient is under control, another slips out of line.

Enter nutritional geometry

A method is needed to understand nutrition for what it is — the association between our biology and “teams” of nutrients that interact to influence our health.

We propose a new approach to nutrition, called nutritional geometry, which does just this.

Nutritional geometry offers a new tool to model diets as mixtures of nutrients, foods, meals and menus, and in this way helps researchers and health professionals to understand how the dietary balance influences health. It can also help individuals to manage their diet, by changing the goal from eating diets “high in this nutrient” or “low in that”, to eating a diet that is balanced in nutrients.

3 pieces of rocket on a plate Photo: One message is clear: we need to reduce our consumption of high energy, nutrient-poor snack and junk foods and beverages. (iStockphoto/bopav)

We can now look forward to clearer messages around the relationships between nutrients, foods, diet and health.

In the meantime, one message is clear. Rather than focus on which nutrient to leave out of the diet, we need to reduce our consumption of high energy, nutrient-poor snack and junk foods and beverages. By any definition, these spell trouble for healthy eating.

Professor Stephen Simpson is academic director of the Charles Perkins Centre at the University of Sydney and will present a keynote address at the Dietitians Association of Australia National Conference in Sydney today. Professor David Raubenheimer is the University of Sydney’s Leonard P Ullmann Chair in Nutritional Ecology.



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