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Will Low Carb Kill You? What The Research Actually Says


Low-carb diet linked to early death, medical study suggests.

USA Today knew this headline — posted August 20th, 2018 — would get serious clicks[*]. Who could resist reading more?

The article covered a new study — published just four days prior — in which researchers tracked 15,428 middle-aged adults over 25 years. Data from this study, originally published in the medical journal The Lancet, found that the lowest carb group also had the shortest life expectancy[*].

If you’re familiar with low-carb diets, this finding might seem odd. Study after study shows that low-carb and ketogenic diets promote weight loss, glycemic control, insulin sensitivity, brain function, exercise performance, and a slew of other desirable changes[*][*][*].

Good science, in other words, strongly suggests that low carb diets are healthy. But the Lancet data seems to indicate otherwise.

So what should you believe? Are low carb diets healthy or potentially fatal?

Before you ditch your healthy fats and load up on rice and bread, you’ll want to keep reading.

Here’s what’s coming:

To set the stage: a brief history of carbs, fat, and mass confusion.

How Low Carb Became Taboo

The fat myth has many moving parts. Let’s start at the beginning.

Ancel Keys And the War On Fat

Some 70 years ago, a doctor named Ancel Keys presented his research to the World
Health Organization. To set the stage, the U.S. saw a shocking rise in heart disease from the early 1900s to the 1960s.

By the time Ancel Keys was put to the task of figuring out what was causing these numbers to rise, heart disease was becoming an epidemic.

Keys hypothesized that saturated fat was to blame. Saturated fat was an easy target that many people could wrap their heads around. Fat makes you fat, right? And obesity leads to heart disease.

The problem was that Keys based this claim on somewhat random, poorly controlled population data from several countries. Populations that ate less saturated fat — Italians, for instance — had lower rates of cardiovascular disease (CVD)[*].

But observational data is known for being generalized, flawed science. It basically means that researchers are going around asking people what they’re eating. And humans are notoriously bad at accurate self-reporting[*].

Today we know a LOT more about nutrition science and how different diets affect your metabolism, your blood sugar, weight loss, and other health markers. Many of these have debunked Keys’ hypothesis. For instance, researchers have found:

  • No link between saturated fat intake and heart disease[*]
  • An inverse correlation between saturated fat and stroke incidence[*]
  • Saturated fat actually protects against alcohol-induced liver damage[*]

Still, the anti-fat myth persists.

The American Heart Association Supports Old Science

The American Heart Association, for instance, recommends replacing saturated fat with vegetable oils and whole grains[*]. The American Diabetes Association recommends a similar diet — rich in whole grains and “moderate” sugar — to treat diabetes[*].

But these recommendations haven’t fixed anything.

If anything, it’s irresponsible advice because the link between sugar consumption, obesity, and type 2 diabetes is now undeniable[*]. By the way: having type 2 diabetes — and the obesity, high blood sugar, and insulin resistance that comes with it — vastly increases your risk of heart disease.

But it doesn’t stop with CVD. Insulin resistance also increases your risk for cancer, neurodegenerative disease, and liver disease[*][*]. Mitigating disease risk, then, means lowering blood sugar, maintaining a healthy weight, and improving insulin sensitivity.

Fortunately, there’s a diet that does all these things — and surprise surprise — it’s not a high carb, low-fat diet.

It’s a low carb, high-fat ketogenic diet.

The Benefits Of Low Carb Keto

When you eat a high carb diet, your blood sugar stays elevated[*]. And when your blood sugar remains elevated, your insulin stays elevated too.

Insulin’s job is to get glucose out of your blood and into your cells so your cells can use it for energy production. But too much blood glucose and insulin will stop doing its job.

Translation: high carb diets lead to chronically elevated blood sugar and insulin levels. This is called insulin resistance — and it’s the beginning of diabetes.

You want your cells to be sensitive to insulin, not insulin resistant. You want low blood sugar, not hyperglycemia. You want to be lean, not obese.

You want, in other words, to be healthy.

A low carb ketogenic diet can help. Here’s how.

Why A Low Carb Diet Is Great For You

#1 Stimulates Weight Loss

When you eat fewer carbs, your blood sugar levels decrease. Which means your insulin levels decrease. And when you’re pumping out less insulin, that means less fat storage.

Another effect of keto? Less circulating ghrelin, your hunger hormone[*]. Less ghrelin, fewer cravings.

So. What happens when you:

1) Store less fat

2) Experience fewer cravings?

Right: effortless weight loss.

(Most of these studies are randomized controlled trials — the gold standard of science)

  • A very recent study showed that low carb diets can improve metabolism and reduce cravings[*]
  • Healthy women on a very low carb diet lost more weight than women on a calorie-restricted low-fat diet[*]
  • Sixteen young people lost more weight on a low carb diet than a low-fat diet throughout 12 weeks[*]
  • Athletes that took ketone salts during a cycling session burned more fat than placebo-fed controls[*]
  • A 24-week ketogenic diet improved body composition and blood lipids in obese people[*]

But cutting carbs doesn’t just improve your metabolism — it also improves your cognition.

#2 Increases Cognitive Performance

When insulin gets low, your body makes a switch. Instead of burning glucose, it starts burning fat[*].

And when you burn fat, you produce ketones. Like glucose, ketones cross the blood-brain barrier to fuel the brain. But unlike glucose, ketones don’t impair cognition.

Here’s what glucose does to your brain. Researchers gave 49 people either a placebo or sugar (glucose) drink, then administered a series of cognitive tests[*]. Results? The sugar group did much worse, and it was thanks to glucose.

Ketones, on the other hand, boost brain activity. Ketone-fed rats are better maze navigators[*], and elderly adults get smarter after ingesting medium chain triglycerides (MCTs) — fatty acids that stimulate ketone production[*].

#3 Helps Prevent Brain Disorders

Ketogenic diets can also help with conditions like Alzheimer’s and epilepsy. Here are a few examples from the literature:

  • As the brain ages, it gets worse at using glucose — and this functional decline has been linked to Alzheimer’s disease. Ketone-utilization, however, does not decline with age. Because of this, a ketogenic diet may be therapeutic for Alzheimer’s[*].
  • Ketones increase mitochondrial function in the brain — another potential way to combat Alzheimer’s[*]
  • Children with epilepsy had fewer seizures, less anxiety, and better cognition after four months on a ketogenic diet[*]

Okay, so low carb keto diets are good for your brain. How about your heart?

#4 Cardiovascular Health

First of all, this is not medical advice — and you should consult a savvy cardiologist to manage your CVD risk.

That said, obesity is a huge risk factor for heart disease — so anything that helps you lose weight, like a ketogenic diet, also benefits your heart[*].

There are reports, however, that a high-fat keto diet can elevate LDL particles. LDL particles are known to cause CVD, so you shouldn’t take this concern lightly.

But in a controlled study, a six-week keto diet didn’t affect LDL, and actually improved the following cardiovascular markers in non-obese men[*]:

  • Insulin (decreased on keto)
  • Triglycerides (decreased on keto)
  • LDL Cholesterol (unaffected on keto)
  • LDL particle size (got bigger on keto — a good thing — you want bouncy, fluffy LDL particles)

Another group of researchers compared the effects of a low-fat calorie-restricted diet vs. a very low carb (VLC) non-calorie restricted keto diet in obese women[*]. Results? Both groups los more weight and experienced improved blood pressure, insulin, and LDL.

Not bad for eating as much as you like.

#5 Exercise Performance

One concern with low-carb diets is that they may sap your performance or prevent muscle building.

But this concern has been unfounded for some 40 years. Yes, in his famous 1983 study, Steve Phinney and his colleagues showed that — after six weeks of keto adaptation — cyclists performed better on their bikes[*].

Why? Because adapting to fat spares muscle glycogen. You can go harder for longer.

But wait. Don’t you need carbs — and the resulting insulin bump — to put on muscle?

Nope. When it comes to muscle synthesis, low carb keto diets outperform high carb western diets[*]. Two reasons why:

  1. The amino acid leucine (from protein) synergizes with ketones for muscle growth
  2. Ketones prevent muscle loss — useful for early humans needing strength on a hunt

But hold on, there are more benefits still.

Other Benefits Of Low Carb Keto

The list of keto benefits could go on for pages, but you’re eager to review The Lancet study — so here’s a shortened version:

  • Potential cancer treatment — ketone supplements shrink tumors in mice (cancer cells love sugar, but can’t run on ketones)[*]
  • Anti-Inflammatory — ketones act as signaling molecules (HDAC inhibitors) to decrease systemic inflammation[*]
  • Anxiety therapy — ketones improve cognition and mood in a mouse model of Alzheimer’s[*], and epileptic children on a ketogenic diet have fewer seizures and less anxiety[*]
  • Neuroprotection — having ketones in your blood can protect against brain injury[*]
  • Lower blood sugar — keeps you out of fat storage, insulin resistance mode

By now you’re probably wondering: with all these benefits, how could low carb diets possibly kill you?

Before turning to The Lancet, however, it’s important to get some terminology straight.

Low Carb Diets Aren’t Always Keto

All the benefits listed above? They were from very low-carb, high-fat diets, aka, a ketogenic diet.

By calories: keto is about 60% fat, 30% protein, and 10% carbs[*]. You can increase your fat and adjust your protein intake, but your carbs must stay very low.

Here’s the crucial point. Just because keto is always low carb and high-fat, that doesn’t mean low carb diets — or high-fat diets — are always keto.

A low carb diet, for example, might also be low in fat. But you’re probably not going to get into ketosis that way.

The inverse is also true. High-fat diets — often vilified in the press — are not always low carb. In fact, most rodent studies that slam high-fat diets use mouse food that’s high in fat and fructose.

Of course high-fat, high-sugar diets are going to cause weight gain, insulin resistance, and liver disease[*][*].

But the media tends to leave out the part about the fructose — jumping straight to the consensus that high-fat diets cause obesity.

To further complicate matters: low carb diets aren’t always low carb diets. Huh?

Sad but true. Depending what academic journal you frequent, low carb can be anywhere from 0% to 40% of calories from carbohydrate.

40%? Definitely not keto. Yet 40% was, surprisingly enough, the low carb cutoff in The Lancet study[*]. Almost half of your calories from carbohydrates is not considered low carb.

To summarize, here’s what keto is not:

  • A low carb low-fat diet
  • A high-fat high carb diet
  • A “low carb” diet with over 10% of calories from carbs

If you get this straight, you’ll cut through most of the inaccurate science about keto, low carb, and high-fat diets.

Speaking of inaccuracy, what about that Lancet study?

Should You Trust The Lancet Data?

A brief summary of that paper now[*].

Researchers followed 15,428 people for 25 years, tracking both diet and mortality data. By the end of the study period, 6,283 of the participants had died.

The researchers split this mortality data by total carb intake. They found that both low carb (<40% calories) and high carb (>70% calories) diets were linked to earlier death.

If you were a low carb 50-year-old, the authors claimed, you’d live about four years less than a 50-55% carber in your age bracket. Fairly significant.

But before you reach for your box of crackers, you’ll want to understand a few things about this study. Then you can decide if the authors’ conclusion makes sense.

#1 It’s Based on Observational Data

The Lancet study was based on observational data, not a controlled experiment. This is a problem for two reasons:

  1. Researchers were using self-reported data (which is notoriously inaccurate)
  2. If you don’t take lifestyle and other factors into account, it’s impossible to isolate the effects of carb intake on mortality.

In fact, these uncontrolled variables probably worked against the low carb group. Low carbers were more likely to:

  • Smoke cigarettes
  • Be male (higher mortality rate than women)
  • Be overweight
  • Have diabetes
  • Eat fewer plants
  • Be sedentary

Perhaps a low carb diet wasn’t the killer. Maybe it was smoking, obesity, or lack of exercise.

Here’s another observational study linking animal fat intake to prostate cancer[*]. But when other researchers controlled for the uncontrolled variables — smoking, alcohol, sedentary life — the link between dietary fat and cancer disappeared[*].

#2 Low Carb Wasn’t Low Carb

Ketogenic diets are very low carb — less than 10% of calories. That’s the benefits zone.

The Lancet “low carb” cohort, however, used 40% carbohydrate as a cutoff. Nowhere near keto. And so, at the very least, the Lancet data says nothing about the ketogenic diet.

Another issue? Daily carb intake was self-reported, sometimes going back years.

Can you remember what you had for dinner three years ago? Neither could the participants.

#3 Correlation Isn’t Causation

Fun fact: You could say that a larger shoe size correlates with reading comprehension. Does this mean sasquatch — or some guy resembling him — is breezing through Tolstoy?

Obviously not. Think for a moment: what variable might explain this correlation?

It’s age. Babies have tiny feet and can’t read. Adults have bigger feet and can. Presto, the correlation appears.

The same logic applies to the Lancet data. Low carb diets were correlated with early death, but this says nothing of what caused that early death.

What could explain the shorter lifespan of the low carb group? Maybe smoking, fewer veggies, or gender.

Or maybe alcohol.

#4 There’s No Data On Alcohol Consumption

When people drink more, they tend to eat less — especially fewer carbs.

It’s true: higher alcohol intake — a known mortality risk factor — is linked to lower carb intake[*].

Unfortunately, the Lancet study researchers didn’t bother collecting data on alcohol consumption. But if they did, you’d likely have another reason to throw out their findings.

To summarize: the Lancet study makes for a good headline, but it’s useless information. Hopefully, the above analysis soothed any of your low carb fears.

Not all studies, however, are like the Lancet study.

How To Spot A Sound Scientific Study

As you’ve seen, research on low-carb and keto diets is all over the map. Sometimes low carb isn’t low carb. Sometimes keto isn’t keto. So how can you use good science to make better decisions for your health?

So what, exactly, makes a high-quality study?

  • It’s not observational: observational studies are notoriously inaccurate and based on bad data
  • It includes one or more control groups: you need a control group for comparison (often a low-calorie group for keto studies)
  • Proper selection of participants: you need diabetic participants — not healthy participants — to test the effects of keto on diabetes
  • Random assignment of participants into groups: randomization helps minimize researcher bias
  • A hypothesis: i.e., “a ketogenic diet stimulates weight loss”
  • A defined outcome measure: like blood glucose — recorded at baseline and follow-up to the effect of the intervention

In addition to these criteria, what makes a good keto study?

  • Sufficient adaptation time: switching from glucose to fat often takes 4-6 weeks. So, studies that test the effects of keto after a week are bunk.
  • Under 10% of calories from carbs: that usually translates to 30 grams or fewer per day
  • 60% of calories from fat: not as much fat as it sounds like
  • Enforced dietary adherence: participants don’t need to be spoon fed or kept in a controlled bubble, but you want to ensure they’re sticking to the dietary guidelines of the study
  • Ketone measurement: if you aren’t producing ketones, you aren’t doing the ketogenic diet right

Okay, time to put it all together and look at a proper keto study.

Proper Keto Research: A Case Study

Researchers randomized 84 obese or diabetic people to eat one of two diets: low calorie and low carb ketogenic.

The hypothesis: That a keto diet would reduce blood glucose — as measured by hemoglobin A1c — in the diabetic population[*].

So far, they’ve nailed the high-quality study checklist:

  • Non-observational
  • Control groups
  • Proper selection
  • Random assignment
  • Testable hypothesis
  • A specific outcome measure

Back to the study.

To ensure dietary adherence, researchers provided detailed nutrition instructions and held weekly meetings for the duration of the 24-week study. The keto group ate less than 20g carbs per day, and around 60% of calories from fat. Ketones were measured via urine testing.

Check, check and check to the good keto list:

  • Diet adherence
  • Adaptation time
  • Proper carb and fat percentages
  • Ketone measurement

Finally, the results. Not only did blood glucose improve in the keto group, but body weight and HDL improved too. Plus, many keto participants were able to drop their diabetes meds.

“Lifestyle modification using low carbohydrate interventions,” conclude the researchers “is effective for improving and reversing type 2 diabetes.”

Now there’s a conclusion you can trust.

Will Low Carb Diets Kill You?

These days, you can’t escape the low carb hate. Even Reader’s Digest has jumped aboard — publishing a reference-free article called Why Low-Carb Diets Aren’t The Answer on November 9th of this year[*].

But Reader’s Digest, USA Today, and many others are merely broadcasting their confusion. They’re confusing correlation with causation. They’re mistaking low carb for keto. And they’re leaning heavily on bad science.

They’re leaning, in particular, on the recent Lancet paper — a poorly-designed observational study with a highly clickable conclusion.

Yet the Lancet study proves nothing. To prove low carb diets kill you, you would need randomized controlled trials showing some mechanism — changes in specific blood biomarkers or a decrease in lifespan — in conjunction with that style of eating. If you’re waiting for these trials, you might be waiting a long time.

While you’re waiting, check out the good science on low carb ketogenic diets. Controlled trials showing weight loss, lower blood sugar, improved insulin sensitivity, decreased inflammation, better brain power, and decreased disease risk — all from going keto[*][*][*].

It’s hard to see how any of these changes would shorten lifespan. It’s easier to imagine the opposite.

Ultimately, of course, the choice to go low carb is yours and yours alone. Hopefully, this article will inform that choice, helping you continue — onwards and upwards — towards better health.

READ NEXT: How Fast Will I Lose Weight On A Ketogenic Diet?


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