You’ve probably seen the headlines: Low-carb diets may shorten your life. Low-carb diets may not be healthy in the long run. Low-carb diets may do more harm than good… The list goes on. What’s the deal: Is a low-carb diet healthy?
As the diet pendulum has recently swung in favor of low-carb diets—thanks in part to the rise in popularity of the very-low-carbohydrate ketogenic diet—this jaw-dropping news is like a figurative slap in the face. And the diet debates rage on.
Are the headlines true? Or, is this yet another case of the media exaggerating the findings of scientific research?
The Recent Study That Stirred the Pot
With all the buzz about keto, low-carb diets have once again risen in popularity. As a result, the diet debates have seemingly hit an all-time high. This is not the first time, nor will it be the last that we’ll be discussing low-carb vs. low-fat diets and which is better and healthier.
Most recently, a new study published in The Lancet Public Health added ammunition to the diet wars. It found that both low-carb diets (<40% of calories from carbs) and high-carb diets (>70%) were associated with increased risk of mortality.1 (This is science speak for death.) The researchers studied the dietary intake of 15,428 American adults (aged 45 – 64) over the course of 25 years. They found a moderate carb intake of about 50 – 55% of calories seemed to be the sweet spot for minimizing the risk of mortality.
Perhaps more striking, the study found low-carb diets that favored more animal-based foods increased the risk of mortality compared to low-carb diets more heavily plant-based. These actually decreased the risk of mortality.
This not the first time such a finding has been reported. In a 2010 study published in the Annals of Internal Medicine, researchers examined data from the NHANES study (including over 120,000 men and women). They also found a low-carb diet based on animal sources was associated with higher all-cause mortality. On the flipside, a plant-based low-carb diet decreased the risk of cardiovascular disease and all-cause mortality.2
This is particularly interesting given the current rumblings about the carnivore diet. And on the flipside, there’s been growing interest in vegan and vegetarian menus.
Certainly, there are some noteworthy limitations to these studies. For starters, they are observational in nature and don’t represent a cause-and-effect relationship. However, if we want to speculate about mortality, clinical trials are not necessarily feasible given the long duration required.
Another huge limitation is that these studies rely on dietary recall. This involves the participants reporting exactly what and how much they ate for a certain period of time. For instance, in the most recent Lancet study, diet was only assessed at two time intervals, spanning a 6-year period. Yet dietary patterns can change substantially during 25 years.
Considering those snapshots were meant to be representative of the entire time period—not to mention that people are notoriously inaccurate when self-reporting food intake—it’s no wonder these findings are being heavily scrutinized.
The generalization that low-carb diets are not healthy is catchy (albeit inaccurate, especially if you don’t take into account the food sources). Yet, one compelling finding is that, when restricting carbohydrate intake, replacement of carbs with predominantly plant-based fats and proteins seems to be a healthier long-term approach to promote healthy aging. In other words, food quality matters—shocker!
What Is “Low-Carb” Anyway?
To answer the question, Is a low-carb diet healthy, one of the first steps is to actually define exactly what “low-carb” is.
This, my friend, is not quite as simple as you might think. There’s not even a clear-cut definition. Even among the scientific community, the lines are blurry with “low-carb” meaning quite different things to different groups.
Let’s be honest: That’s not low-carb. At best, it’s moderate-carb. On the other hand, some have set the cutoff definition for a low-carb diet at 26% of calories, or less than 130 grams of carbohydrates per day.5 And still others suggest a true low-carb diet limits carbs to 30 – 70 grams per day—or less. If there’s one type of well-defined low-carb diet, it’s the very-low-carbohydrate ketogenic diet, which limits carbohydrate to less than 30 grams per day.
Confused? Me too, especially considering that low-carb advocates were chanting, “I told you so!” when the results of the Prospective Urban Rural Epidemiology (PURE) study were recently published in The Lancet. The PURE study, which involved over 135,000 participants (aged 35 – 70) from 18 countries across 5 continents over 10 years, found high carbohydrate intake was associated with increased risk of death.6
This study also demonstrated that “total fat and individual types of fat were related to lower mortality.” And the researchers concluded by saying, “Global dietary guidelines should be reconsidered in light of these findings.” It’s no wonder low-carb zealots were shouting from the mountaintops.
Something that got lost among the headlines, tweets, and one-liners, however, was that a “high-carb” intake meant consuming more than 60% of calories from carbs—quite a far cry from even the most lenient “low-carb” definition.
Having said all that, there’s little question that “how much” matters. Not just as a relative amount (i.e., percentage of caloric intake) but also in terms of overall intake. And along those lines, the former can influence the latter. For example, some find that lower-carbohydrate diets increase satiety (i.e., feelings of fullness and satisfaction). This ultimately helps manage overall intake.
Arguably more important than “how much” is “what” you eat. Put differently, we don’t eat “carbs”; we eat food. And frequently, low-carb diets promote better food choices and overall diet quality. With low-ish carb diets, you tend to see an increase in the consumption of vegetables, fruits, lean meats, poultry (including eggs), nuts, seeds, and healthier fats and oils.
For example, in the PURE study, most participants who consumed a high-carb diet (≥ 60% of calories)—who also tended to come from low- and middle-countries—ate predominantly refined sources (e.g., refined flour-based products, added sugar).
Another typical benefit of low-carb diets: Addition by subtraction. Although certainly not always the case, by telling people what not to eat, low-carb diets can naturally lead to reduced consumption of ultra-processed, high-carb junk food (e.g., refined grains, added sugar). And hopefully to no one’s surprise, another finding of the PURE study was that higher fruit, vegetable, and legume consumption was associated with a lower risk of death from all causes.7
So, What Does Healthy Mean to You?
To add confusion to the “Is a low-carb diet healthy” question, another point of contention is how you define “healthy.”
- Is it weight loss/management and body composition?
- Is it diet quality?
- Is it a certain health marker like blood cholesterol, triglycerides, blood sugar, insulin, and inflammatory markers?
- Is it a hard endpoint like death?
- Is it a more subjective variable like feelings of well-being or sleep quality?
- Or, is it a bit more obscure like how diet impacts your stress levels, or perhaps even more important, your relationships?
YES. The truth is that any of these examples—and a litany of others—may be relevant and important to you depending on where you are (and where you want to be) on your health and wellness journey.
Along those lines, depending on which direction one is leaning, we could certainly “cherry pick” studies to tip the scales in favor of or in opposition to low-carb diets. In fairness, low-carb diets (with varying degrees of carbohydrate restriction) typically perform as well or better than low-fat diets when it comes to weight loss and markers of heart health (e.g., blood lipids, blood pressure) and metabolic function (e.g., blood glucose, insulin). 8
In a review of 23 weight-loss trials, for example, published in the American Journal of Epidemiology, researchers found both low-carb and low-fat diets led to weight loss, reduced waist circumference, and improved metabolic risk factors with no significant differences between diets. They concluded, “These findings suggest that low-carbohydrate diets are at least as effective as low-fat diets at reducing weight and improving metabolic risk factors. Low-carbohydrate diets could be recommended to obese persons with abnormal metabolic risk factors for the purpose of weight loss.”4
In a separate review published in the journal Nutrients, researchers from the University of Florida examined the evidence for current popular diets. They looked at low-fat (e.g., Ornish, DASH), low-carb (e.g., Atkins), and everything in between (e.g., Zone, Mediterranean). Interestingly, they found the Atkins Diet, which emphasizes carbohydrate restriction, “showed the most evidence in producing clinically meaningful short-term and long-term weight loss.”9
Having said that, a randomized controlled trial published in the Journal of the American Medical Association comparing the Atkins, Ornish, Weight Watchers (low fat), and Zone (low carb) Diets found that “each popular diet modestly reduced body weight and several cardiac risk factors” after one year.10
One of the best and most reliable examples is the A TO Z Weight Loss Study, a randomized trial conducted by a group of Stanford researchers led by Dr. Christopher Gardner. In the trial, the researchers compared 4 popular weight-loss diets—Atkins (low carb and high fat), LEARN (low fat), Ornish (low fat), and Zone (technically considered low carb)—and they found that women following the Atkins diet lost more weight and experienced more favorable metabolic effects after 12 months compared to the other diets.11
In Dr. Gardner’s most recent study—The DIETFITS clinical trial, which randomized 609 healthy overweight or obese adults to a healthy low-fat or a healthy low-carb diet for 12 months—published in the Journal of the American Medical Association, both diets led to similar weight loss and metabolic health improvement (e.g., reduced fasting glucose and insulin). Notably, the low-carb diet did lead to more favorable improvements in HDL cholesterol and triglycerides.12
One of my favorite aspects of the DIETFITS trial was the emphasis on diet quality. Dr. Gardner and his team put a tremendous emphasis on high dietary quality for both diet groups. This is important because traditional low-fat diets often lead to reduced diet quality due to the low-nutrient density of heavily processed, convenient, pre-packaged low-fat foods (e.g., refined grains, added sugar).
The Best Examples of the “Low-Carb” Lifestyle
Now, if you want to know how healthy a low-carb diet can be, you don’t have to look any further than two of the most popular approaches to eating. The Mediterranean- and Paleo-style diets consistently rank highly for diet quality and beneficial health outcomes. 13,14 For more specifics about these two diets, please see the following articles:
Truth be told, neither of these styles of eating have specific macronutrient targets. However, studies estimate that, for Paleo-style diets, carbohydrate intake is roughly 35 – 40% (ranging as high as 65%), while total fat intake may be as high as 35% (or as low as 20%). 3,15
While Mediterranean-style diet composition can vary significantly across regions and time of year, researchers estimate that about 37% of calories come from fat and 43% of calories come from carbohydrate.16
While there’s no question I’d consider these “moderate-carb diets” according to the loose definitions we have, they fall within bounds of what most would consider “low carb.” (Of course, there’s certainly room for disagreement.) There are other more important reasons I wanted to highlight Mediterranean- and Paleo-style diets:
- They both emphasize eating REAL food (i.e., whole, minimally processed food).
- Diet composition reflects seasonality and food availability.
- They fall into the context of a much broader set of healthy living practices.
Along those lines, Mediterranean and Paleo lifestyles are known to involve regular physical activity, sharing meals with others, enjoying life, being outdoors, properly managing stress, and incorporating plenty of purposeful rest and sleep.
For example, a hunter-gatherer fitness plan looks quite a bit different and more elaborate than the typical workout program. Meanwhile, the Mediterranean lifestyle involves staying physically active the natural way—gardening, yardwork, chores, and walking or riding bikes to go places.
So…Is a Low-Carb Diet Healthy?
Chances are the diet debates are far from over. Yet, it’s important to understand why they rage on—beyond giving the media headline-grabbing fodder and offering folks something to argue about on social media. This type of research (called epidemiological research) plays a significant role in the development of health policy.
You see, health organizations charged with the (arguably unreasonable) responsibility of drafting broad, population-based dietary guidelines use this data to make the most reliable general recommendations they can. Unfortunately, this is an incredibly challenging and dynamic task. If not unfair and misleading.
Having said that, in my opinion, there’s no question that a lower carb diet can be quite healthy. Attention-grabbing headlines notwithstanding. With hesitation, here are some general takeaways about carbohydrate intake:
• A moderate carb intake (roughly 40% of caloric intake) is usually a good starting point, with some folks doing better with slightly more and some with a bit less.
• Typically, carb intake should be inversely proportionate to activity levels. In other words, more active folks can usually use carbs more efficiently while people who are sedentary tend to be less tolerant of carbs.
• Generally speaking, carb intake should be proportionate to metabolic health and metabolic flexibility. Leaner folks typically tolerate carbs better while people with more belly fat tend to be more carb resistant.
• We don’t eat carbs; we eat food. Along those lines, arguably more important than “how much” is what types of foods are making up your carb intake. There’s a big difference between eating veggies, fruits, legumes, and true whole grains (which are packaged with a ton of other beneficial nutrients like vitamins, minerals, and fiber) versus products made with highly processed carbohydrates (e.g., “foods” made with refined flour and/or added sugars).
• Let me repeat: Regardless of how many carbs you eat, most people would be well-advised to consume more real, whole, minimally-processed plant-based foods. And if you are restricting carbohydrate intake, this may have even greater relevance, as a plant-based low-carb diet may be a healthier option than a low-carb diet based on animal sources.
• While we can make some ballpark estimates for carbohydrate intake, let’s not get tunnel vision. Specifically, don’t think you have to eat 40% carbs every day of the week every week of the year. It’s okay to cycle carb intake. There may be benefits to doing so. For example, some people find it beneficial to consume more carbs on days they’re more active. And from a hunter-gatherer perspective, there’s little question that our ancestors likely went periods where they ate more or fewer carbs based on seasonality.
• Along those lines, there may be applications to using very-low-carbohydrates diets (VLCD) as a tool for certain folks. For example, people who have overgrowth of unhealthy gut microbes, who struggle with FODMAPs, or who have less-than-stellar metabolic health may all find carbohydrate restriction leads to significant improvements. After which time, they may find that a gradual re-introduction of more carbs (from healthy sources, of course) is both tolerable and beneficial.
• While it’s not at the top of the totem pole, carb timing is a potentially relevant and useful tool for more advanced folks to consider. For example, insulin sensitivity tends to be highest at the first meal of the day (e.g., morning). And exercise is a surefire way to increase carb tolerance (i.e., eat carbs after exercise).
With all that said, one thing we have learned about nutrition over the years is that individual differences most certainly apply. Self-experimentation is often the best bet to find what works optimally for you. Keep in mind, however, that the process is dynamic. What worked at one point in your journey may not be the current recipe for success.
What have you found works best for YOU? I’d love to hear your feedback. Please share your comments below!