Last week, my staff nutritionist Laura Schoenfeld wrote a guest post for my blog called “Is a Low-Carb Diet Ruining Your Health”. Perhaps not surprisingly, it has caused quite a stir. For reasons I don’t fully understand, some people identify so strongly with how many carbohydrates they eat that they take offense when a suggestion is made that low-carb diets may not be appropriate for everyone, in all circumstances.

In these circles low-carb diets have become dogma (i.e. a principle or set of principles laid down by an authority as incontrovertibly true). Followers of this strange religious sect insist that everyone should be on low-carb or even ketogenic diets; that all carbohydrates, regardless of their source, are “toxic”; that most traditional hunter-gatherer (e.g. Paleolithic) societies followed a low-carb diet; and, similarly, that nutritional ketosis—which is only achievable with a very high-fat, low-carb, and low-protein diet—is our default and optimal physiological state.

Cut through the confusion and hype and learn what research can tell us about low-carb diets.

On the other hand, I’ve also observed somewhat of a backlash against low-carb diets occurring in the blogosphere of late. While I agree with many of the potential issues that have been raised about low-carb diets, and think it’s important to discuss them, I also feel it’s important not to lose sight of the fact that low-carb diets can be very effective therapeutic tools for certain conditions and in certain situations.

With this in mind, here are 7 things I think everyone should know about low-carb diets.

#1: Paleo does not equal low-carb, and very low-carb/ketogenic diets are not our “default” nutritional state, as some have claimed.

Some low-carb advocates have claimed that most traditional hunter-gatherer societies consumed diets that were very low in carbohydrates. I’ve even seem some suggestions that nutritional ketosis was “the norm” for these cultures.

These claims are false. The majority of studies have shown that traditional hunter-gatherer (HG) societies typically consume between 30–40% of their total calories from carbohydrate, though the range can vary between 3–50% depending on the population studied and the latitude at which they live. (2, 3) The only HG societies observed to eat fewer than 20% of calories as carbohydrate were those living at latitudes quite distant from the equator, often in marginalized environments where fruits, vegetables, starches, and honey were not readily available.

Yet even these cultures—such as the traditional Inuit—often made an effort to obtain carbohydrates from berries, corms, nuts, seaweed, and tubers whenever they could, as Richard Nikoley has recently detailed on his blog. What’s more, contrary to popular claims, studies have shown that it’s unlikely the Inuit spent much time—if any—in nutritional ketosis. Their high protein intake would have prevented ketosis from occurring. (5)

So, while ancestral diets were certainly lower in carbohydrate than the diet currently recommended by the USDA (45–65% of calories), they were not typically “very low” in carbohydrate (<15% of calories). With virtually no historical examples of human beings following ketogenic diets for any significant length of time, and few examples of very low-carb diets, it’s difficult to imagine how these diets could be considered our “default” nutritional state or the optimal approach for most people.

#2: Low-carb diets are incredibly effective in certain situations

Lest low-carb advocates think that I am anti-low-carb, I’d like to reiterate that both the research and my clinical experience suggest that low-carb diets can be incredibly effective therapeutic tools for certain conditions.

These conditions include (but aren’t limited to):

Overweight and obesity
High blood sugar, metabolic syndrome, diabetes (both type 1 & type 2)
Traumatic brain injury
Epilepsy
Parkinson’s disease
Alzheimer’s disease
Other neurological conditions
PCOS
I have personally witnessed some remarkable transformations using ketogenic diets therapeutically in my practice. I recall an 84 year-old woman who came to see me complaining of dementia and early-onset Alzheimer’s. She was losing her memory and cognitive abilities at an alarming rate. After just two weeks on a ketogenic diet, this progression not only halted, it reversed: her memory returned, her mind was sharper, and she was far less confused and disoriented. Her family (and her doctor) were stunned, and could hardly believe the changes they were seeing.

Yet as impressive as very low-carb (VLC) and ketogenic diets can be in certain situations, that does not mean that these diets may not have some undesirable side effects over the long term—some of which we’re only beginning to understand. For example, as I discussed with Jeff Leach from the American Gut project in a recent podcast, some preliminary research suggests that long-term ketogenic/VLC diets may cause adverse changes to the gut microbiota. (6) In addition, a new paper soon to be published in the journal Cell by two Stanford microbiologists indicates that diets low in “microbiota-accessible carbohydrates (MACs)” contribute to modern, inflammatory disease. (7)

The phrase “microbiota-accessible carbohydrates” refers to the various fibers found in fruits, vegetables, starchy plants, nuts, seeds, legumes, and other foods that are poorly absorbed by us, but can be utilized as a food source by our intestinal bacteria. It’s worth noting that many of these fibers are found in foods with moderate to high carbohydrate content—foods that would typically be excluded on very low-carb diets.

It’s important to note, however, that the beneficial bacteria-starving effects of ketogenic/VLC diets can be at least partially offset by consuming non-digestible, fermentable fibers like resistant starch and non-starch polysaccharides that don’t count toward daily carbohydrate intake. This is something I recommend to all of my patients following low-carb diets)

#3: The fact that ketogenic/VLC diets work therapeutically for certain conditions does not make them appropriate in all circumstances, for all people

This assumption is a basic failure of logic, but it’s remarkable to see how often it happens. A person has a life-changing experience with a VLC diet, so they assume that their friend will have a similar experience. Or a clinician that works primarily with people suffering from neurological conditions has great success with ketogenic diets, and then makes the assumption that all people (regardless of their health complaints) will benefit from them.

This is akin to saying that since people with hemochromatosis (a genetic condition that causes iron overload) need to limit their iron intake, everyone should consume foods that are low in iron.

The belief that “everyone” will benefit from one particular dietary approach—no matter what it is—ignores the important differences that determine what is optimal for each person. These include variations in genes, gene expression, the microbiome, health status, activity levels, geography (e.g. latitude and climate), and more.

When it comes to diet, there is no one-size-fits-all approach.

#4: Some people do better with low-carb diets than others

If you understand #3 above, then this should not come as a surprise.

Some people may thrive on a long-term, low-carb diet. I have patients and even a family member in this category. And maybe you’re one of them too. But that doesn’t mean everyone will have this experience. If you talk to practicing clinicians who work with patients on a daily basis, or spend any amount of time in internet forums or the comments sections of nutrition blogs, you’ll find numerous reports from people who either experienced no benefit from or were even harmed by following a low-carb diet.

What blows my mind is that the “low-carb zealots” seem completely incapable of accepting these reports at face value. Instead, they’ll argue that anyone who doesn’t succeed with low-carb is either doing it wrong, cheating, or somehow imagining their symptoms.

What’s the more likely explanation here? That everyone who gets worse with a low-carb diet is either incapable of following directions, weak-willed, or delusional? Or that a low-carb diet simply does not work for everyone? You be the judge.

#5: If a low-carb diet works as a therapy in a given condition, that doesn’t mean too many carbs caused that condition in the first place

This is another error of logic that is often made. Here’s an example:

“A low-carb diet is effective for treating type 2 diabetes. Therefore, eating too many carbohydrates led to this condition in the first place.”

This is like saying:

Restricting iron is helpful in hemochromatosis patients. Therefore, consuming too much iron is what caused hemochromatosis in the first place.
A low-FODMAP diet helps patients with Irritable Bowel Syndrome (IBS). Therefore, eating FODMAPs caused IBS in the first place.
A low-histamine diet alleviates the symptoms of histamine intolerance. Therefore, histamine intolerance is caused by eating too many histamine containing foods.
Or, more ridiculously, since wearing a cast on your arm will help the broken bone heal, the reason you broke your arm in the first place is because you weren’t wearing a cast.

It’s true that VLC/ketogenic diets are effective for improving the metabolic markers associated with type 2 diabetes. But that doesn’t mean that eating too many carbohydrates led to the condition in the first place. It is certainly possible (and indeed likely) that eating too many refined and processed carbohydrates, in the form of flour and sugar, contributes to diabetes. But I have not seen a single study suggesting that eating whole-food carbohydrates (e.g. fruit or starchy plants) leads to diabetes or other metabolic problems. On the contrary, reviews of prospective studies looking at the relationship between fruit intake and diabetes have found that those with the highest intake of fruit had the lowest incidence of diabetes. (8, 9)

It is also worth pointing out that virtually all studies performed so far showing benefits of the Paleo diet in conditions like type 2 diabetes and obesity have used moderate carbohydrate (not low or very-low carb) versions of the Paleo diet.

#6: If a low-carb diet is an effective therapy for a condition, that doesn’t mean it’s the only therapy for that condition

There’s little doubt, as I said above in #2, that low-carb diets can be remarkably effective in certain situations. For example, there are numerous studies showing that low-carb and ketogenic diets can help with weight loss and metabolic problems. (10)

However, that doesn’t mean it’s not possible to lose weight and reset your metabolism through other means. Studies have also shown that calorie-restricted diets, protein-sparing modified fasts, and even low-fat diets can also be effective treatments. (11, 12, 13)

This means that it’s not necessarily true, for example, that everyone with type 2 diabetes should be on a low-carb diet. They may be able to reverse their condition by following a high-protein, moderate-carbohydrate, moderate-fat diet (such as the Paleo diet with 32% of calories from carbohydrate in this study), or any of the methods I just mentioned.

#7: Whole-food carbohydrates do not affect the body in the same way as processed and refined carbohydrates

This should be obvious to anyone with a basic understanding of nutrition and human physiology, so I’m amazed at how often I see experts talk about all carbohydrates as if they’re the same.

In #1 above, I referenced studies indicating that most hunter-gatherer societies consumed about 30–40% of calories from carbohydrate. These carbohydrates came from starchy tubers and plants, whole fruit, and in some cases, honey. We also have evidence of specific ancestral populations—such as the Kitava, traditional Okinawans, and Tukisenta—that consumed between 70–95% of calories from whole-food carbohydrate. (14)

Yet despite this liberal consumption of carbohydrates, these people were remarkably lean, fit, and free of chronic, inflammatory diseases like diabetes, cardiovascular disease, and neurological conditions. (15) If carbohydrates cause these conditions, regardless of their source, why don’t we see such conditions in these groups?

What we do see is that these cultures acquire modern disease when they adopt a modern diet and lifestyle, complete with the highly processed and refined foods that characterize it.

When it comes to macronutrients, quality is much more important than quantity for most people.

Final thoughts

I hope this helps to clarify some of the confusion that has surrounded this issue. Low-carb diets are an effective therapeutic tool in certain situations, and one that I (and many other clinicians) use in my clinical practice. That said, it’s equally true that low-carb—and especially VLC and ketogenic—diets are not appropriate in all circumstances, and they are certainly not our “default” or optimal nutritional state.

Sadly, it doesn’t seem to matter how much scientific evidence, clinical experience, and common sense is brought to bear on this question: those who preach and follow low-carb dogma will not be swayed. Ah, well. As they say: “You can’t fight faith with facts.”

Now I’d like to hear from you. What has your experience with low-carb diets been like? Have you had success with them over the long term? Or have they caused you harm? What is your optimal intake of carbohydrate? Let us know in the comments section.

Artificial sweeteners -- promoted as aids to weight loss and diabetes prevention -- could actually hasten the development of glucose intolerance and metabolic disease, and they do so in a surprising way: by changing the composition and function of the gut microbiota -- the substantial population of bacteria residing in our intestines. These findings, the results of experiments in mice and humans, were published September 17 in Nature. Dr. Eran Elinav of the Weizmann Institute of Science's Department of Immunology, who led this research together with Prof. Eran Segal of the Department of Computer Science and Applied Mathematics, says that the widespread use of artificial sweeteners in drinks and food, among other things, may be contributing to the obesity and diabetes epidemic that is sweeping much of the world.

For years, researchers have been puzzling over the fact that non-caloric artificial sweeteners do not seem to assist in weight loss, with some studies suggesting that they may even have an opposite effect. Graduate student Jotham Suez in Dr. Elinav's lab, who led the study, collaborated with lab member Gili Zilberman-Shapira and graduate students Tal Korem and David Zeevi in Prof. Segal's lab to discover that artificial sweeteners, even though they do not contain sugar, nonetheless have a direct effect on the body's ability to utilize glucose. Glucose intolerance -- generally thought to occur when the body cannot cope with large amounts of sugar in the diet -- is the first step on the path to metabolic syndrome and adult-onset diabetes.

The scientists gave mice water laced with the three most commonly used artificial sweeteners, in amounts equivalent to those permitted by the U.S. Food and Drug Administration (FDA). These mice developed glucose intolerance, as compared to mice that drank water, or even sugar water. Repeating the experiment with different types of mice and different doses of the artificial sweeteners produced the same results -- these substances were somehow inducing glucose intolerance.

Next, the researchers investigated a hypothesis that the gut microbiota are involved in this phenomenon. They thought the bacteria might do this by reacting to new substances like artificial sweeteners, which the body itself may not recognize as "food." Indeed, artificial sweeteners are not absorbed in the gastrointestinal tract, but in passing through they encounter trillions of the bacteria in the gut microbiota.

The researchers treated mice with antibiotics to eradicate many of their gut bacteria; this resulted in a full reversal of the artificial sweeteners' effects on glucose metabolism. Next, they transferred the microbiota from mice that consumed artificial sweeteners to "germ-free," or sterile, mice -- resulting in a complete transmission of the glucose intolerance into the recipient mice. This, in itself, was conclusive proof that changes to the gut bacteria are directly responsible for the harmful effects to their host's metabolism. The group even found that incubating the microbiota outside the body, together with artificial sweeteners, was sufficient to induce glucose intolerance in the sterile mice. A detailed characterization of the microbiota in these mice revealed profound changes to their bacterial populations, including new microbial functions that are known to infer a propensity to obesity, diabetes, and complications of these problems in both mice and humans.

Does the human microbiome function in the same way? Dr. Elinav and Prof. Segal had a means to test this as well. As a first step, they looked at data collected from their Personalized Nutrition Project (PersonalNutrition.org), the largest human trial to date to look at the connection between nutrition and microbiota. Here, they uncovered a significant association between self-reported consumption of artificial sweeteners, personal configurations of gut bacteria, and the propensity for glucose intolerance. They next conducted a controlled experiment, asking a group of volunteers who did not generally eat or drink artificially sweetened foods to consume them for a week, and then undergo tests of their glucose levels and gut microbiota compositions.

The findings showed that many -- but not all -- of the volunteers had begun to develop glucose intolerance after just one week of artificial sweetener consumption. The composition of their gut microbiota explained the difference: the researchers discovered two different populations of human gut bacteria -- one that induced glucose intolerance when exposed to the sweeteners, and one that had no effect either way. Dr. Elinav believes that certain bacteria in the guts of those who developed glucose intolerance reacted to the chemical sweeteners by secreting substances that then provoked an inflammatory response similar to sugar overdose, promoting changes in the body's ability to utilize sugar.

Prof. Segal states, "The results of our experiments highlight the importance of personalized medicine and nutrition to our overall health. We believe that an integrated analysis of individualized 'big data' from our genome, microbiome, and dietary habits could transform our ability to understand how foods and nutritional supplements affect a person's health and risk of disease."

According to Dr. Elinav, "Our relationship with our own individual mix of gut bacteria is a huge factor in determining how the food we eat affects us. Especially intriguing is the link between use of artificial sweeteners -- through the bacteria in our guts -- to a tendency to develop the very disorders they were designed to prevent; this calls for reassessment of today's massive, unsupervised consumption of these substances."