DIET WARS
Is a low-carb diet really better than low-fat? Experts weigh in on the debate
Plus the mistakes people always make when going on either diet
Carbs or fat? Many people juggle cutting one or the other down as a means to lose weight or improve overall health.
Debate about which method is better has rattled on for years, with a new study shedding light on the topic.
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It found that eating a zero-carb diet (also known as keto) could help boost the effects of treatment for pancreatic cancer - one of the most deadly forms of the disease.
Scientists at University of California found that mice on a keto diet and drug combination saw the greatest shrinkage in tumours compared to mice on typical diets.
Meanwhile, eating a low-carb diet could help to reduce your risk of type 2 diabetes, heart disease and stroke, research has found.
But on the other hand, experts warn against a low-carb diet (particularly keto) - loved by celebrities such as Kim and Kourtney Kardashian - because of it's potential side effects, such as fatigue, bad breath and potentially even heart disease or kidney stones.
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Last week, researchers at the University of Bath found following the keto diet over 12 weeks raised cholesterol levels and reduced number of beneficial bacteria in people's guts.
Meanwhile, low-fat - a diet familiar with those who lived through the 90s - could helpy you live longer, according to a study last year.
Based on dietary data from over 370,000 US adults, its findings show that middle-aged people with low-fat diets had an 18 per cent lower mortality rate than those on low-carb eating patterns.
Experts speaking to The Sun reckon there’s more nuance to the discussion than simply concluding one diet is better than the other.
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Rhiannon Lambert, a registered nutritionist (), said: “These particular two diets have been floating around in and out of the media for a long time.
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“They come into popularity because of bold claims around weight loss.
“Anything your body tries suddenly, is going to be a bit of a shock to the system and usually people see short term results.
“But then that tends to peter off and 90 per cent of dieters put back on the weight that they originally lost and more.”
Let’s take a look at the two diets on their own...
LOW-CARB DIET
What are carbs?
Thinking of carbohydrates, your mind might zero in on bread, pasta, cakes.
But there are different types: refined - which are processed and nutrient poor - and unrefined, which are minimally processed and higher in fibre.
Some people might avoid carbs as a whole because they fear they’re fattening.
But, Dr Sarah Jarvis, a GP and clinical consultant to, says it’s the refined variety that’s unhealthy to eat in large quantities.
These include starchy carbs, which are “basically anything white”, such as “white bread, white flour, white pastries, bright white rice”.
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Fizzy drinks and refined sugar can also be classed as sugary carbs.
As for unrefined carbs, they include wholegrain bread and pasta, non-starchy vegetables, pulses and legumes.
Rhiannon explains: “Carbohydrates are essentially sugars that provide our bodies with energy.”
Carbs in the form of glucose are our body’s preferred source of fuel - “our brain loves it and uses it to function every single day,” says Rhiannon.
Benefits and risks
For type 2 diabetes sufferers, a low carb meal plan can be very effective for short-term weight loss and can even drive the condition into remission, Sarah says.
Dr Duane Mellor, registered dietitian and lead for evidence-based medicine and nutrition at Aston University, says the low-carb diet quite seem "appealing".
“It can seem like an easy way of reducing the calories in our diet,” he says.
“It’s a very simple piece of advice [cut back on carbs] and for a large number of people it can work out to lose weight.”
But he says following a low carbohydrate diet isn’t “automatically healthy".
Strict low-carb dieters sometimes go further than cutting out white bread, pasta and pastries; they’ll also eschew fruit, vegetables and grains.
Sarah says this risk you becoming deficient in vitamin B, vitamin C, phosphorus, magnesium, selenium, and other micronutrients that are important to your body’s function.
You could risk making existing liver problems worse because of the amount of fat you metabolise and “constipation is really a big issue because you’re not eating enough fibre,” Sarah says.
Everybody can benefit by reducing or, as much as possible, cutting out refined carbs.
Dr Sarah Jarvis
She adds: “If you look at the longer term, it's not necessarily that good for helping you lose weight, because frankly, it's quite boring.”
A diet that is boring is one you’re unlikely to follow for long.
When the body is lacking in carbohydrates, which provide glucose, it needs to turn to other fuel sources.
In a process called gluconeogenesis, the body turns fats and proteins into glucose when there are no carbohydrates available.
Sarah explains: “Ketones are what we produce when your body is converting other sources into glucose.
“Instead of relying on glucose that comes from carbohydrates, it is forcing your body to rely on a different form of energy. ”
But according to Rhiannon, only carbohydrates can pass through the blood-brain barrier.
As a result, people who go on low carb diets can feel irritable and fatigued because their brain isn’t getting the energy as efficiently, Rhiannon explains.
Plus, there’s not much data on what happens to our bodies if we follow the diet for more than a short stint, Sarah adds.
Bottom line on low-carb
Health advice points towards minimising or getting rid of refined carbs instead of all carbs.
Sarah states.“There isn't a one size fits all, but overall as a rule, everybody can benefit by reducing or, as much as possible, cutting out refined carbs.”
Opt for unprocessed and whole grain foods instead, as well as vegetables, fruit, beans, lentils and pulses, Sarah notes.
LOW-FAT DIET
What is fat?
Fat mainly comes in two forms in food: saturated and unsaturated.
The former is typically known as the unhealthy kind, while the latter is ‘healthy’.
The bulk of foods high in saturated fat come from animal sources and include fatty cuts of meat, dairy products such as butter, hard cheese and ice cream, biscuits, cakes, and palm and coconut oil.
Unsaturated fats are mostly found in oils from plants and fish, as well as nuts. They include olive oil, avocados, walnuts, almonds and cashews, as well as oily fish such as salmon.
These foods are often the sources of fatty acids your body needs but cannot make themselves - omega 3 and omega 6 fatty acids, which are important to making the membranes of our cells healthy.
Saturated fat, on the other hand, may lead to high cholesterol, a fatty substance in the blood, which drives up your risk of heart disease and stroke among other problems.
Indeed, it can lead to all sorts of health problems, but it is also key for making hormones, such as testosterone, oestrogen, cortisol, Duane said.
Fat also helps the body absorb vitamin A, vitamin D and vitamin E.
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Benefits and risks of a low-fat diet
Like the low-carb option, you’re likely to lose weight at first, if you cut out fat.
Fat has the highest amount of calories per gram compared to protein and carbohydrates. So there are 90 calories per 10g of fat compared with 40 calories for 10g of protein or carbs.
That means going ‘low-fat’ will see you remove a lot of calories from your diet, if you currently eat a lot of fat.
Without focusing meals on high protein with a good portion of carbohydrates, however, there is a chance you’d feel hungry after meals quickly.
According to Rhiannon, “a lot of people don’t categorise fat, they just say fat’s fat,” and might make the mistake of cutting both healthy and unhealthy fats when they go on a low-fat diet.
For example, ‘low-fat’ yoghurt has little nutritional value compared to normal or ‘full-fat’ yoghurt, which is more likely to be filling.
You’d also miss out on the benefits of nuts - a powerhouse of vitamins and minerals - avocados, and olive oil.
While a person may lose a bit of weight at first on low-fat, it probably won’t be a sustainable change for the long-term, Rhiannon said.
Especially if they don’t make other changes to their diet to account for the lack of fat.
Bottom line on low-fat
Though you do need some fat, Sarah notes, “most of us have far more [of it] than we need”, and eating lots of saturated fat can drive up cholesterol levels in your blood, upping your risk of heart disease or stroke.
In moderation, unsaturated fats can lower the ‘bad’ cholesterol in your blood and increase your ‘good’ cholesterol, according to the GP.
“What we’re talking about here is reducing your intake of saturated fat, that's basically meat and dairy fats,” Sarah says.
Though you do need some fat, she notes “most of us have far more [of it] than we need”.
So where does that leave us?
The answer to whether low-carb and low-fat diets are good for people is “somewhere in the middle”, Duane says.
“There’s not one right answer for everyone.
“If you are making a deliberate change to try and eat healthy, whichever direction you take it in - low-fat, low-carb, other changes - [you need to think]: what am I adding into my diet to make it healthy? How am I going to continue to enjoy this diet?”
These ‘conscious food choices’, he argues, are more important what kind of diet you go for: “it’s how you build a healthy diet around that change”. .
For Sarah, it’s the ‘quality’ of a carb or fat that matters, as she says: “A low-fat diet where you eat lots of refined carbs is going to be bad for you.
“Whereas a low-fat diet where you're eating unrefined carbs - and particularly a low-fat diet where you're eating low saturated fats but adding more unrefined carbs - is good for you.”
Of course, studies have compared low-fat and low-carb diets for weight loss results.
published in the journal Nature Medicine split 20 participants into a low-fat diet (plant–based) or a low-carb diet (animal-based) for two weeks.
The meals and snacks were matched in calories, but people could eat as much or as little as they wanted.
Those on the low-fat diet ate up to 700 calories fewer per day than those on low-carb.
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People lost weight on both diets, but those on low-fat lost more body fat. However, the low-fat diet resulted in higher blood glucose and insulin levels compared with the low-carb diet.
The researchers concluded that there are benefits to both diets; the low-fat diet helps curb hunger and appetite, but the low-carb diet was better for steady blood sugars and insulin - at least, in the short term.
What does the NHS recommend?
NHS guidelines on fat and carbohydrate consumption
Starchy food should make up just over a third of the food we eat, NHS guidance states, while fruit and veg should make up another third.
Opt for higher fibre or wholegrain varieties, such as wholewheat pasta and brown rice, or simply leave the skins on potatoes.
Starchy foods are a good source of energy and the main source of a range of nutrients in our diet such as fibre, calcium, iron and B vitamins.
Though some people think starchy foods add to weight, they contain fewer than half the calories of fat.
The NHS notes that all types of fat are high in energy and should be eaten in small amounts: try to go for lower-fat and lower-sugar dairy products and chocolate, cakes, biscuits, sugary soft drinks, butter, ghee and ice cream should be consumed less often.
Choose unsaturated oils and spreads, and eat in small amounts.
Aim to eat at least five portions of fruit and veg daily, which can be fresh, frozen, tinned, dried or juiced.
And try to have at least two portions of fish every week, one of which should be oily, such as salmon, sardines or mackerel.
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