04 Sep PURE headline fodder
Are carbs trying to kill you?
Anyone who’s seen any nutrition headlines in the last week – or any headlines for that matter will have read about the PURE study.
Here’s some of my favourites:
Eating a low-fat diet 'increases your risk of dying young by 25%
Low fat diet kills
Huge new study casts doubt on conventional wisdom about fat and carbs
So, sounds pretty straight forward – can I go eat ALL the butter now?
Not so fast. Let’s start at the beginning.
What was the study?
It’s an ongoing observational study, looking at what over 135,000 people in 18 countries ate over a period of about 7.4 years and comparing this with their outcomes for all causes mortality (we all die, soz – this just looks at what the participants died from and whether they lived as long as they might be expected to) and cardiovascular events like strokes and heart attacks.
What did they find?
There were a few interesting outcomes from the study results…
Those who ate diets that were high in carbohydrates ( more than ~60% of intake) and low fat had a 23% higher risk of dying (from anything) than those in the study with a lower carbohydrate intake and higher fat intake.
Higher intakes of saturated fat were associated with a lower risk of stroke and vice versa.
Fruit, vegetables and legumes:
Maximum benefits for all cause mortality and fruit, veg and legume intake was around 3-4 portions / day. Benefits didn’t seem to increase the more fruit, veg and legumes were eaten.
Put that butter down! Let me explain a bit more.
So, the study did yield some pretty interesting results, though there were some bits of it – as with any research – that still need a bit of explaining.. and in a way the Daily Fail needn’t bother with.
One major point was to do with carbohydrates – in particular, the difference between complex and refined carbohydrates. That’s the difference between your wholegrain bread and your bag of sherbet; two quite different sources of carbohydrate. The study authors themselves noted in the discussion that it would have been useful to assess the difference between the two.
We already know that too much refined carbohydrate may not be ideal – as we’re missing out on the nutritional benefit of the rest of the whole food like vitamins, minerals and fibre. For many of the people surveyed though, it may not be realistic for them to increase their fat intake nor reduce their carbohydrate intake for reasons beyond their control, like money.
Fruit, vegetable and legume intake was ‘..inversely associated with total mortality in most regions‘ – so that means that an increase in consumption reduced the risk of mortality. The benefits seemed to level off at about 3-4 portions a day though. This means that higher intakes were associated with better outcomes, but it is conflicting with other data we have.
It’s still interesting though and the fruit and veg intake recommended is about the same as our current fruit and veg intake in the UK (4/day for adults, 3/day children).
Location Location Location
Another point is the countries the participants came from – North America and Europe only contributed 14,000 participants overall to the study – whereas China contributed 42,000 and lower income countries like India, Pakistan and Bangladesh contributed 29,590.
It is brilliant to see a study conducted across such a wide range of countries and incomes, the data is invaluable, however it is also difficult to extrapolate when looking at our own dietary patterns.
In these countries, lower incomes and the prohibitive cost of meat and animal products means that lower fat intakes can translate into less varied diets and higher carbohydrate intakes – as staples like white rice are cheaper.
Eating less saturated fat (which comes from mainly animal sources) also means that people in these countries may have been eating less meat, fish and dairy products. The majority of participants had a saturated fat intake of less than 10% of total kcals.
These food products contain protein and lots of other vitamins and minerals like iron and zinc; and so diets lacking in these may lead to malnutrition – and as such an increase in this mortality thing we’ve been talking about.
Compared with the UK and other higher income countries, the majority of participants in this study may also have had limited access to affordable, decent healthcare, medicines and even clean water – again, quite important when looking at mortality.
It’s interesting to note that the lowest carbohydrate intakes in these groups were around 46% – this is NOT a low carbohydrate diet and only ~2% less than our current average carbohydrate intake in the UK according to current NDNS data. The highest reported carbohydrate intakes in the UK are only around 62% of total energy, still just encroaching the 60% recommendations from the PURE study.
The highest fat intakes recorded in the study are around 35% – almost the same as our average UK intake. Lowest total fat intakes seen in this study were around 10% – compare this with our lowest fat intakes of around 22%. Those whose diet consisted of more than 23% kcals from total fat saw beneficial effects – as the graphs below point out, that’s nearly everyone in the UK already and well within our recommendations.
So, do we need to change our current guidelines? Let’s look at the figures
Comparing current UK dietary recommendations, UK intake (from NDNS data) and PURE study recommendations.
PURE study carbohydrate recommendations 0%
Current carbohydrate intake UK 0%
Current carbohydrate recommendations UK 0%
PURE study total fat recommendations0%
Current total fat intake UK0%
Current total fat recommendations UK (upper) 0%
Well, look at the data – it’s pretty in line, right? As for an upper limit for fat; this is some good data that we can add to the pile and keep building on. We should always be looking at our recommendations and that’s why they do change… as confusing as that may be.
Saturated fat then?
So, the study did find that there was in inverse relationship between total fat intake and mortality and saturated fat intake and stroke risk – so the higher saturated fat intake, the lower the risk and vice versa. This is very interesting and adds weight to the question mark over our current saturated fat recommendations – but it’s worth still considering the overall diet of participants and the whole foods that contribute to their saturated fat intakes, as previously mentioned.
HOWEVER the highest intakes percentage for saturated fats were those eating ~13.2%. That’s only a couple of percent over our guideline recommendations and our own average intake is currently ~12% in the UK. The much higher end of the intakes at 19% that were reported in the NDNS may still have negative effects on health, especially considering our main sources of saturated fat: biscuits, cakes, pastry and confectionary.
Long Story Short
Oh, it’s oh-so dull, I know – but moderation wins out. Generalising study results and formulating recommendations is incredibly difficult – requirements vary widely across populations according to many things; age, activity levels and gender amongst them.
Unfortunately there is no way of ascertaining cause and effect with just an observational study and there is no one macronutrient or super food that’s going to wave a magic wand and make us all live longer. Diet, lifestyle and nutrition are about more than that – just enjoy your butter and enjoy your bread (well, as long as you like it!).
I think the authors at Science Daily nailed it with this headline:
If you want to take a look at a beautifully written and more in-depth look at the study, I fully recommend Nutrition Wonk’s blog post on the subject (and many other subjects!).