Diet debate: Low-fat or high-fat – does it matter? – BBC News

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Is fat the great evil of our time responsible for seducing us into an early, extra-wide, grave with its delicious succulence?

Or is it as misunderstood as it is mouth-watering? And in need of a welcome return to our plates?

As the campaign against sugar has ratcheted up over the past year or two, there have been growing voices trying to redeem fat.

For decades it has been labelled public adversary number 1 and a “low-fat” food label is used to convince us that what we’re buying is healthy.

The problem is low-fat can mean veggies or only clever marketing for “we took out all the fat and then pumped it full of sugar”.

So there I was having a moment in the supermarket – a bathtub of low-fat yoghurt in one hand and a full-fat one in other – mulling which was actually better for me.

If I had a third hand, it would have been scratching my head. And I’m not alone.

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“When there’s a huge wall of yoghurt, even I find it paralysing, ” told Susan Jebb, a nutrition professor at the University of Oxford.

When you take the fat out of products, particularly dry ones like cake or cookies, then something has to replace it.

“It tends to be sugar – the calories in digestives and low-fat digestives are almost the same, ” Prof Jebb continued.

“Lots of yoghurts are rammed with sugar, that is the thing that riles me about yoghurt.”

There is a simple answer with yoghurt – a few brands are both low in fat and sugar, although I need to chuck in a little bit of fruit to make it palatable.

But what about the case that we should be feeing more fat?

Some have argued that the message about cutting all fats when discussing bad saturated fats from processed foods was oversimplified.

While others have induced the case that favouring carbohydrates in our diet – particularly refined carbs like white bread and pasta, is playing havoc with our hormones to increase the risk of kind 2 diabetes and building us pile on the pounds.

More from our Diet Debate series:

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Fatty joy?

We do all require fat in our diet – it contains essential fatty acids and is important for assimilating fat-soluble vitamins such as A, D and E.

The question has always been: “How much fat should we eat? ” And the mantra has been low-fat, high-carb.

The World Health Organization advises that between 30% and 35% of our calories should come from fat arguing there is “no probable or convincing evidence” that the total amount of fat in our diet is altering health risks of cancer or cardiovascular disease.

So when it comes to the total amount of fat( and there is a separate debate when we come to consider different types of fat) it’s actually a question of how it affects our waistlines.

And fat is certainly calorific.

A gram of fat is worth around nine calories – twice the amount as carbohydrate or protein at four calories per gram.

Too much fat, like too much of anything, will attain you put on weight and it is incredibly easy to overeat calorie dense foods.

So it appears to be an easy target for people trying to lose weight.

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Image caption Appetising?

“There is very good evidence that if you cut down on total fat it causes a small reduced by weight, but it’s not big, ” told Dr Lee Hooper from the University of East Anglia in the UK.

She conducted a large review of 32 separate trials, involving around 54,000 people.

It depicted people who shifted between 5% and 10% of their calories away from fats lost around 2kg during the studies.

However, she is not convinced the weight-loss is actually down to fat but more an expression of the results of people guessing more about what they eat and avoiding burgers, ready dinners and other processed foods.

“I suspect they’d do exactly the same thing if they targeted sugar, ” she concluded.

So how do diets compare when we target carbs?

Doctors at the Harvard School of Public Health in the United States reviewed 53 weight loss trials involving 68,128 people.

The outcomes, published in the Lancet medical journal, showed that both low-carb and low-fat approaches led to decent weight-loss.

But those feeing comparatively more fat actually lost marginally more weight.

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Image caption Some fats are relatively healthy, but still calorie dense

Dr Deirdre Tobias, who led that survey, told me: “If you’re trying to reduce your calories and you take out the fat then you get a lot of bang for your buck, but that strategy clearly doesn’t play out.

“Fat has been villainised because there’s a mentality that ‘fat stimulates you fat’. I suppose our proof pretty much puts a fingernail in that coffin.”

She is not saying that carbs are the villain instead, but that the best diet is the one you can actually stick with – some people would find it pretty easy to give up on white bread and pasta while others would find it impossible.

But she did warn that focusing on simply avoiding fat risked missing out on known beneficial foods – such as nuts, oily fish and olive oil – or convincing yourself that a low-fat muffin is healthy.

Cutting carbohydrates rather than the fat has furthermore demonstrated some benefit in patients with type-2 diabetes, at the least for a short while.

When refined carbs are digested they rapidly lead to a spike in blood sugar levels and in turn of the hormone insulin. People with type 2 have difficulty controlling their blood sugar levels so avoiding the spike could help in theory.

Although analyses indicate the advantage of cutting carbs was not sustained in the long-term.

Rethink involved?

In the UK the total amount of fat being eaten is broadly in line with recommendations, but with slightly more saturated fat than advised.

Dr Hooper concluded: “I would be saying we don’t required to cutting down on fat, but we do need to think of the type of fat.”

That’s an issue we’ll consider on Wednesday when we ask: “Is butter back? “

But clearly “theres never” going to be health advice to only pour cream down our throats and polish off all the pies and cookies we can.

Even drowning a salad in olive oil could lead to weight gain.

Going overboard on fat, just as having too much sugar or refined carbohydrate, is a bad thing. Sugar is just stealing the headlines at the moment.

“The reality is that nutrition goes and goes in waves, we’ve had a fat wave and we’re for sure in a sugar hysterium, ” says Prof Jebb.

She says she frets “enormously” when people reduce all the nation’s health problems to being “all about fat or all about sugar”.

We need to think about both.

Follow James on Twitter.

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