Avoid­ing diet ex­tremes, not carbs or fat, is key

More prob­lem­atic are over-eat­ing and too much re­fined sugar, James McCor­mack says.

Montreal Gazette - - OPINION -

The world has seen a plethora of “ex­perts” pro­vid­ing nu­tri­tional ad­vice that sounds de­fin­i­tive and ev­i­dence-based. Many of us have lived through all the rec­om­men­da­tions: low fat then high fat; salt is a prob­lem, then salt is no prob­lem; eggs are good, then they are bad; but­ter is very bad, mar­garine is good, then but­ter is good again; high carbs, then no carbs — and so on.

This be­fud­dle­ment has led both health-care pro­fes­sion­als and mem­bers of the gen­eral pub­lic to make rec­om­men­da­tions — or even changes in our own di­ets — that, from afar, re­sem­ble a great cos­mic yo-yo.

So here we go again.

A few weeks ago, a large (18 coun­tries, five con­ti­nents, 135,000 peo­ple) and long (7.4 years) co­hort study on nu­tri­tion was pub­lished in the Lancet. The re­sult­ing head­lines were full of hy­per­bole: “low fat di­ets could kill you” and “huge diet study shows carbs not fats are the prob­lem.”

But when it comes to in­ter­pret­ing nu­tri­tional ev­i­dence, you shouldn’t just read the head­lines. The devil is al­ways in the de­tails.

For starters, a co­hort study like this can­not de­ter­mine cause and ef­fect, but only give a sug­ges­tion as to what might hap­pen when pop­u­la­tions con­sume vary­ing amounts of macronu­tri­ents — car­bo­hy­drates, fats and pro­tein. The peo­ple stud­ied in­gested a broad range of macronu­tri­ents (any­where from 45 to 75 per cent of calo­ries from car­bo­hy­drates, 10 to 20 per cent from pro­tein and 10 to 35 per cent from fat). The in­ves­ti­ga­tors then looked at the as­so­ci­a­tion between the per­cent­age of macronu­tri­ent in­take and ma­jor car­dio­vas­cu­lar dis­ease and over­all death.

What they found is that there was no as­so­ci­a­tion between the per­cent­age of macronu­tri­ent in­gested over 7.4 years and the chance of a per­son de­vel­op­ing car­dio­vas­cu­lar dis­ease — a ma­jor cause of over­all dis­ease and death.

An as­so­ci­a­tion was seen for over­all death. How­ever, even then, an in­crease in death was only as­so­ci­ated with those peo­ple who in­gested carbs at the high­est per­cent­age (around 75 per cent) of the ranges stud­ied, or those who in­gested pro­tein or fats at the low­est per­cent­age (around 10 per cent) of the ranges stud­ied.

Im­por­tantly, the in­crease in the risk of death was only around one to two per cent higher for peo­ple at th­ese “ex­treme” ranges. In other words, this study seems to sug­gest that the macronu­tri­ent com­po­si­tion of a diet isn’t a big de­ter­mi­nant of what makes a diet healthy or not.

Now let’s put this co­hort study in con­text along­side ran­dom­ized con­trolled tri­als, the high­est form of ev­i­dence. Many might be sur­prised to learn only three large tri­als look­ing at im­por­tant clin­i­cal out­comes have ever been done in nu­tri­tion: the 1994 Lyon Diet heart study (pri­mar­ily men with car­dio­vas­cu­lar dis­ease); the 2013 PREDIMED (men and women with­out car­dio­vas­cu­lar dis­ease); and the 2006 Women’s Health Ini­tia­tive (women with­out car­dio­vas­cu­lar dis­ease).

The first two stud­ied ver­sions of a Mediter­ranean-type diet and found that fa­tal plus non-fa­tal car­dio­vas­cu­lar dis­ease was re­duced by around eight per cent over two years and around one per cent over four years, re­spec­tively. The WHI found a lower-fat diet had no im­pact on car­dio­vas­cu­lar dis­ease or any health out­come over eight years.

Tak­ing th­ese stud­ies all to­gether sug­gests, over­all, as long as a per­son doesn’t eat at the ex­tremes of any macronu­tri­ent, they should be fine.

So, to all those peo­ple who pros­e­ly­tize low carbs, high carbs, low fat, high fat: there’s no strong ev­i­dence to favour one over the other.

There are two im­por­tant caveats. One, there are clearly peo­ple who do not eat in a healthy man­ner, but by far their big­gest is­sue with food is the amount in­gested. And two, ev­i­dence is also fairly clear when it comes to ex­ces­sive in­take of over-pro­cessed food and re­fined sug­ars.

The good news is there’s no yo-yo this time. Look­ing at the ev­i­dence, many of us are eat­ing a rea­son­able diet when it comes to macronu­tri­ents.

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