Will A Low Carb Diet Shorten Your Life?

Have you seen these headlines?

Meat-heavy, low-carb diets can ‘shorten lifespan’: study – CTV

Low-carb diets can shorten life expectancy: study – CBC

Low-carb diet linked to early death, medical study suggests – USA TODAY

Low carb diets shorten your life unless you are mostly vegetarian, study suggests – The Independent

This comes at a time when everyone and their dog is raving about the benefits of the ketogenic diet (low carb/high-fat), and its’ ancestral relative – the Paleo diet, both which are top trending diets of 2018.

And for good reason…

Low-carb diets have accumulated quite the track record lately, with some strong, well-designed research studies showing:

Not to mention this large-scale, international study from 2017 with over 130,000 participants that showed a strong relationship between low carb/high fat intake and longevity… the EXACT OPPOSITE of the current headlines!

Confused? Yeh, me too!

Fake Health News

The current headlines making their way through the internet and social media are fuelled by this research study published last week in The Lancet Journal Of Public Health.

In it they claim they have found a strong association between how many carbohydrates consumed and one’s lifespan, where more is better. At least to a point.

Now, to be honest, I was immediately sceptical of these claims given my understanding of optimum human nutrition, but I wanted to give the authors a fair shot… maybe their work has been taken out of context or exaggerated by the mainstream media?

And although that is certainly true – media outlets are becoming increasing desperate to get your attention – the real dirt is in the details. I want to share a couple of the biggest flaws with you so that you can better interpret the stories and ultimately make better decisions when it comes to what you eat and feed your family.

Observations, Not Experiments

The first thing to note is that the study in question is what’s called an epidemiologic study. This type of health research is super useful, however it has major limitations.

The basic steps are to take a large group of people, measure a whole bunch of things and then follow them for a long time to see what happens.

And when the researchers start analysing the data, they look for relationships that appear to exist between the behaviors and characteristics of the participants and the primary outcomes being measured (eg cause of death).

In this case, the researchers wanted to know if there was a relationship between how many carbohydrates people ate (on average) and their lifespan.

However, this is where the major drawback comes in: This type of research is limited to identifying correlation, not causation. In other words, just because two things appear to be related doesn’t mean that 1 causes the other.

This is because there could be other factors (called confounding variables) that haven’t been measured that contribute to the relationship.

This is where it gets interesting.

The participants who fell into the low-carb group (the ones who lived less long) also turned out to be more likely to “…have high body-mass index (overweight or obese), exercise less during leisure time, have high household income, smoke cigarettes, and have diabetes.”

And these are only the confounding variables that were measured. It says nothing about sleep habits, what kinds of jobs they did or how stressful they were, the quality of their social connections or any number of other factors that have also been associated with poor health outcomes.

In other words, it’s very difficult to tease out that how many carbs they ate alone created the difference in lifespan.

Garbage In Garbage Out

If you’re still with me, you may be asking – “How do they even know what foods the participants ate?”

Great question.

Imagine having to recall what you’ve eaten, on average, over the past 2 years. How accurate would that be?

I’m not sure about you but I have a hard time remembering what I ate last night, let alone last year!

And yet that is exactly the method used to collect the data here – called Food Frequency Questionnaires. Unfortunately, this method of collecting diet records has been shown to be inherently inaccurate.

Not only do people tend to have a hard time recalling what they ate, it turns out people who identify as ‘healthy’ tend to under-report the food they think are bad (like red meat, fatty, fried foods etc) and over-report on the so-called healthy foods they eat (like vegetables, fruits, grains… aka CARBS).

On top of that, those subjects who identify as healthy eaters also tend to employ many other healthy habits – referred to in this kind of observational research as the ‘Healthy User Bias.’ This has been shown to further degrade the quality of this kind of research.

In other words, the individuals in the high-carb group would be more likely to employ a whole host of other healthy behaviours like prioritizing exercise, not smoking, drinking less, better sleep habits, better stress management among countless other possible confounders.

Conclusion: Science Is Complicated

There are several other challenges with this study but I think I’ve made my point.

My concern when I read these kinds of studies (and the over-simplified headlines they generate) is that people will actually believe them and make choices based on them.

Eating 50% of your calories from carbohydrates is effectively sticking to the standard American/Canadian diet that has been recommended for the past 60 years. And for as long as we’ve been adhering to these dietary standards, our health as a society has consistently declined. More people than ever before suffer from chronic illnesses like diabetes, cancer, heart disease and autoimmune conditions.

Of course, that may just be an inaccurate correlation on my part… but at least for me, that’s not a risk I’m willing to take!

Want to learn a simple, evidence-based approach to fuelling your body? Check out our free Eat By Design Quick Start Guide!

Dr. John MacPhee is a Chiropractor, speaker and passionate health and wellness expert. He has inspired thousands of people to take control of their own health using the Life By Design method. Dr. John is co-owner of The Wellness Group, the largest Life By Design Certified Chiropractic office in Canada. Apart from full time practice, John maintains a busy speaking schedule, with a particular emphasis on improving productivity and focus at work. Otherwise you can find John training hard at CrossFit 613, exploring Gatineau Park, or holed away studying the latest research at various cafes across the west end.

Will A Low-Carb Diet Shorten Your Life?