What science says about your New Year’s diet plans

The chances are that you overdid it over Christmas and New Year… or did it just right, depending upon your perspective. Still, January is the month to buckle down – both figuratively and hopefully in the sense of tightening belt buckles – and lose the weight gained through holiday excesses.

There are plenty of options for wannabe dieters, all of which sound plausible enough from a distance, but what does science have to say about the best way to lose weight for the long haul?

BMI isn’t everything

The first question to ask is, of course, “do you need to lose weight?” For that, we have a handy metric endorsed by the NHS: the body mass index (BMI). The trouble is that the BMI is pushing 150 years old and has severe limitations. For one thing, it doesn’t deal well with extremes, meaning that short people are more likely to be told they’re thin, while tall people are often called overweight. It also has some laughable outliers, particularly when dealing with the extremely muscular, unless you believe Dwayne “The Rock” Johnson to be obese.

Nonetheless, it remains a decent starting point if nothing else, which is probably why we’ve stuck with it, despite better alternatives being mooted (although, to my mind, anything called the corpulence index is dead on arrival in terms of mass acceptance). You can try a number of these formulas to see what the consensus on your weight is.

If it looks like you do need to lose weight, it shouldn’t be rocket science: if you burn more calories than you put in, you’ll lose weight. But are all diets are created equal?

Fat isn’t the enemy it once was

The most obvious place to start, you’d assume, is fat intake: nominative determinism sees to that. However, science is gradually coming to the consensus that fat isn’t the demon it once was. The health advice liberally doled out in the 1970s stated fat should compose no more than 30% of people’s daily food intake, but it was revealed last year that this was totally flawed. While nobody is actively arguing that fat is good for you, the study concluded that the “dietary advice not merely needs review, it should never have been introduced”.

Indeed, this seems to match up with other recent lab experiments which come back to the overall calorie total. Just three months ago, a study was published in The Lancet that revealed people on low-fat diets lost roughly the same amount as people on diets with comparable calorie consumption who consumed high proportions of fat.

The risks of fad diets

Individual dieting trends haven’t had a huge amount of research into them, but in general there’s one big drawback to quick weight loss: it has a tendency to return with interest, once a normal diet is resumed.

This isn’t guaranteed – I can personally vouch that the three stone I lost in 90 days in 2012 hasn’t returned – but it’s certainly something to keep an eye on. A meta-analysis from the University of California examined 31 long-term weight loss studies and discovered that while participants lost 5-10% of their body weight within six months, a significant number of them regained more weight than they’d lost back in the five years that followed.

Of course, this analysis doesn’t account for the individual merits of specific diets. It’s a little too early to expect detailed breakdowns on the latest diets’ effectiveness and long-term impacts. The Paleo diet is a popular one, which insists its participants eat like cavemen by cutting out refined foods. There are all kinds of positive benefits inherent in cutting out sugar altogether, but the validity of the premise that our ancestors ate better has been called into question. On the other hand, it does involve reducing carbohydrates, a strategy that even Harvard’s School of Public Health endorses as being effective in the short term. Indeed, a study from Tulane University found that those on a low-carbohydrate diet lost 7.7 more pounds than those on a low-fat one over the course of a year.

Intermittent fasting has its place

One incredibly popular routine is the 5:2 diet or similar “intermittent fasting” plans, which have a comparatively strong body of research looking into them. The idea of these diets is that you spend a few days eating very little (two days of 500-600 calories, in the case of the 5:2 diet) and the remaining time eating your usual diet. As long as you don’t go crazy in your days off, the theory argues, you’ll see the pounds fall off quickly and painlessly.

And that’s broadly the findings of the research into the diets, too. A review of studies on intermittent fasting, published just last year, found that across the six studies, subjects lost an average of 9% of their body weight over six months and a huge 80% were able to stick with it. Another study from 2011 found that overweight women lost similar amounts to more traditional dieting techniques. There are even some studies that suggest fasting could help protect against Alzheimer’s and schizophrenia, although so far this has only been observed in rodents.

Naturally, diabetics are advised to steer clear of intermittent fasting plans, given the likelihood of blood-sugar levels dropping with long periods of not eating.

Cut out the booze and soft drinks

One thing that all the diets have in common is some kind of moderation in terms of drinking. Soft drinks – including fruit juices – tend to be packed full of sugars that contribute to our daily calorie target without doing anything to our appetite. Switching to water, wherever possible, is a pretty good solution.

Diet versions of soft drinks – with artificial sweeteners replacing the sugar – are often seen as decent substitutes, replacing the standard 150ish calories with a single one, but there’s reason to ditch these too. A study in the journal Obesity from 2012 revealed that those consuming the most diet drinks put on the most weight. There are plenty of theories on why, but the general consensus is to avoid them where possible.

Then there’s alcohol. The start of the year is a pretty good time for a weight-loss plan, as plenty of people are abstaining from alcohol for Dry January. Indeed, just by ditching booze, you may shift a few pounds. Beer is around 180 calories per pint, while a large glass of red wine will put 160 on. A shot of vodka is just under 100 calories, but if you need a sugary mixer to make it go down easily, you’re back to square one.

Oh, plus a study from last year revealed that alcohol makes food smell more desirable. So not great for the willpower, either. Just say no.

The place for exercise

Then of course, there’s the other side of the classic equation. To lose weight, you need to burn more calories than you consume, so what if you simply up the quantity you’re burning? Anecdotally, I’ve heard a lot of people explaining that the process of weight loss is 90% diet and only 10% exercise. Hard to quantify exactly, of course, but the limited research on the subject seems to back this up. Back in 1997,

That sounds pretty conclusive, but there is something positive to come from exercise: in the long run, those who exercised were more likely to keep the weight off – on average, after a year they kept off five pounds more than those who just dieted.

So perhaps there’s nothing too earth-shattering from the research, but then it is a limited body. As long as the overall calorie rules are followed, there seems to be something to say for personal taste: if you have a sweet tooth you can’t tame, then low-carb routines are almost certainly a no-go for you, while intermittent fasting may be just the ticket if you have the willpower for 48 hours of misery. Whatever your diet of choice, read up on it first and examine testimonials – hopefully they’ll lead the way to a healthier year ahead.

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Images: daBinsi, InvactaHOG, Ronald Surayandej, Ewan Monroe, FrenchTart, Jeff Doe, Jeff Blackler used under Creative Commons