Low-Fat vs Low-Carbohydrate Diet – which is best?


dietDiet is a topic that many of us are interested in. We are often awash with anecdotal stories and so we become inspired to try some fad only to discover that it is both hard and also often fails in the long term to live up to the promises on offer. So how do we work out what is the best choice, what really works?

It’s a vast complex topic and we simply can’t cover it all in one posting. What we can do is to drill down to one question that was recently investigated scientifically.

Which diet is best, low fat or low carbs, does one offer better results or a better outcome in the long term?

A new study has just been published that reviewed the effects of a low-fat vs low-carbohydrate diet over a 12 month period.

Effect of Low-Fat vs Low-Carbohydrate Diet on 12-Month Weight Loss in Overweight Adults and the Association With Genotype Pattern or Insulin Secretion

Basically they asked this question …

What is the effect of a healthy low-fat (HLF) diet vs a healthy low-carbohydrate (HLC) diet on weight change at 12 months and are these effects related to genotype pattern or insulin secretion?

What they discovered is that low-fat vs low carb did not make any difference at all. I confess that this did surprise me, if asked to speculate then I would have leaned towards a low fat diet having a better long-term outcome. However, facts are facts …

In this randomized clinical trial among 609 overweight adults, weight change over 12 months was not significantly different for participants in the HLF diet group (−5.3 kg) vs the HLC diet group (−6.0 kg)

They did also wonder if different people reacted to the diet variations in different ways. Is low-fat something that works for some, and for others low-carb is actually better? The answer to that is also apparently not …

neither genotype pattern nor baseline insulin secretion was associated with the dietary effects on weight loss.

Rather obviously, if you want to lose weight then you do need to modify what is going on.

Think of yourself as a car – as you drive, you burn fuel. To keep rolling you need to pull into a gas station and refuel. If you keep putting more in each day than you burn, then the amount of stored fuel will slowly increase over time.

Until you get to a point where you burn slightly more than you consume then success will be elusive. What this study appears to confirm is that what you cut down on does not appear to matter all that much.

Low-fat vs Low-Carb

Does it really make no difference at all?

If your goal is weight loss and the associated benefits that come with that, then apparently not …

there were no significant between-group differences observed for body mass index, body fat percentage, and waist circumference (Table 3). At 12 months relative to baseline, both diets improved lipid profiles and lowered blood pressure, insulin, and glucose levels

There was one exception. For those on the low-carb-normal fat diet this happened …

The 12-month changes in low-density lipoprotein cholesterol concentrations significantly favored a healthy low-fat diet.

… but that is perhaps not a surprise.

So the bottom line is this …

We conclude that when equal emphasis is given to high dietary quality for both low-fat and low-carbohydrate eating plans, it is not helpful to preferentially direct an individual with high insulin secretion status who is seeking weight loss to follow a lower-carbohydrate eating plan instead of a lower-fat eating plan.

Radical vs Moderate

Sustainability is important. For the study this is how they set things up …

participants were instructed to reduce intake of total fat or digestible carbohydrates to 20 g/d during the first 8 weeks

… Then individuals slowly added fats or carbohydrates back to their diets in increments of 5 to 15 g/d per week until they reached the lowest level of intake they believed could be maintained indefinitely.

Some can and do adopt a very radical approach and go on a crash diet. This is not sustainable. Your body responds to this famine by increasing your hunger to motivate you to pack on the pounds in readiness for the next famine. The best strategy is to opt for the moderate and sustainable where you consume just slightly less than you burn.

The study ran over a 12 month period and so they encouraged the participants to adopt a diet that they could sustain indefinitely.

If you are thinking about adopting a diet for a few months in order to lose a bit of weight loss then you might not be thinking about this correctly. You need to change your diet permanently in a manner that is sustainable.

You should understand that this is not easy. The secret sauce, if you will forgive the metaphor, involves striking the right balance and burning just a little bit more than you consume.

Further Reading – So what does actually work?

Steven Novella writes about this study over on his Neurologica blog, but does additionally offer some rather sensible guidance that is based upon his experience of what works and what does not …

a recent study confirms the finding that after weight loss our hunger increases. Our bodies respond as if we just went through a famine, and so we better pack on the fat while we can to prepare for the next one.

This is why most diets fail long term. Counting on 24/7 will power is a difficult strategy that most people cannot pull off. It is a setup for failure. What predicts long term success is making permanent changes to your lifestyle that are sustainable. Don’t count on will power, for example, have low calorie food (and not high calorie food) in the house for snacking. Change your ordering habits when you eat out. Change your perception of how large a portion is appropriate.

More importantly, find your problem areas and come up with ways to fix them. People have different behaviors, social situations, and resources, and so think about when you consume the most calories and think of ways to mitigate it that you can live with indefinitely. Weigh yourself every week, estimate your caloric intake, and keep people close to you in the loop so they can support you. All these things predict success in long term weight loss.

But don’t think that just changing the balance of macronutrients, or going on that fad diet, is the magic answer. If you do you are overwhelmingly likely to have short term success and long term failure, because you didn’t make permanent changes to your behavior.

And definitely exercise to keep up your muscle mass, metabolism, and for overall health. But don’t expect to lose weight solely by burning more calories. This strategy doesn’t work. It helps, but you need to have portion control to make the math work.

Finally, don’t plan on losing weight quickly. That is not healthy or sustainable. You are better off planning on slow but steady weight loss – 1 to 1.5 pounds per week, for example. This also predicts success.

The good news is there is a lot of research in this area and we actually have lots of helpful information that predicts success in long term weight loss. The bad news is that most of the information out there is not science-based. It is based on selling self-help books, magic diets, and wishful thinking.

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