As a person with type 1 diabetes on a low carb diet, I don’t have serious concerns about my nutrient intake. I feel healthy, and I always endeavor to eat plenty of the ingredients that we are told are nutritional powerhouses: kale, spinach, salmon, avocado, even the occasional beef liver. Even my rare medium carb treats, like dark chocolate and raspberries, show up on these lists of so-called superfoods. But I’ve never gone to the effort of tracking my micronutrient intake, and do wonder what I would learn if I did.
Can you get enough nutrients on the keto diet? Is there anything in particular that you need to watch out for?
THE STUDY
Lucky for us, two Irish researchers have just released a study that touches on this very topic (PubMed summary; full PDF download). While the authors had a different ultimate goal – to examine the effect of blood hematology of athletes on low- and high-carb diets with a view towards athletic performance – the study contains raw data on the nutrient intake of adults on a true keto diet.
This was a test of a real world keto diet, which may make it the first of its kind to include such data. The authors note that previous studies to approach the topic had looked at “low carb” diets that required >80g carbohydrates per day, which wouldn’t allow most eaters to attain nutritional ketosis, or focused on weight loss interventions in which participants ate at a caloric deficit.
For eating guidelines, researchers used the advice in Volek and Phinney’s 2012 The Art and Science of Low Carbohydrate Performance, a canonical text in keto circles. Participants were told to limit carbohydrates to a maximum of 50g per day, and otherwise were recommended to follow mainstream keto advice: avoid polyunsaturated fats (eg vegetable oils), to prioritize organ meats and green leafy vegetables, to take in extra electrolytes, and so on.
On the one hand, we should keep in mind that these were ravenous athletes, consuming about 3,000 calories per day, and they would have found it easier to hit micronutrient goals than would a less active and less hungry person. On the other hand, their very high-fat diet, laden with coconut oil, butter and cream, is likely to be less nutrient dense than a Bernstein-style high-protein diet.
The authors cautioned that their study was not intended to study nutrient deficiency, which requires more complex analysis than is possible from this data. Nevertheless, the figures are interesting and potentially illuminating. Below, we highlight potential nutritional inadequacies that keto dieters should look out for:
Fiber
Fiber consumption on the keto diet declined more than 50%. Not surprising, but the consequences of this are subject to debate. The study authors encourage keto eaters to prioritize low-carb sources of fiber, such as avocados, seeds and leafy vegetables, but other keto advocates dare to suggest that fiber is not as important as previously thought. Indeed, there have been some remarkable studies published, including this one, which shockingly shows that a low- or zero-fiber diet relieved constipation far better than a high-fiber diet.
Sodium
Sodium consumption fell dramatically, by about 50%, from 3,400mg to 1,700mg. How did it drop so much? Likely the fact that the athletes on a keto diet stopped eating so many grains and processed foods. Surprisingly, most of America’s sodium consumption comes from grains and from grain-based dishes such as pasta and pizza.
This may look good on the surface. The American Heart Association sets a recommended daily limit of 2,300mg, and an ideal target of 1,500mg. But those numbers are much-debated, and may even be based on research that has been discredited. Some studies have even shown the very opposite: that sodium intake below 2,300 mg is associated with a hugely increased likelihood of cardiovascular disease and death.
It may be even more important for people on a low-carb diet to target an increased sodium intake. A ketogenic diet “enhances the kidney’s ability to clear extra sodium,” flushing out sodium at an increased rate, which means that keto dieters need to consume even more sodium to compensate. Volek and Phinney recommended that an active keto dieter take in as much 5,000mg per day.
What is most interesting here is that the athletes in this study were specifically advised to consume extra salt, and yet their intake still dropped precipitously. If there’s one takeaway from this exercise, it may be how surprisingly low one’s sodium intake drops when giving up a standard diet of processed, starchy foods.
Magnesium & Potassium
Magnesium intake dropped 25%, but it remained above the recommended daily allowance of 420mg/day. It is often theorized that people on the keto diet need extra magnesium, which is found in nuts and leafy greens in addition to whole grains and legumes.
The same goes for potassium, another electrolyte of special interest to keto dieters. While avocados and spinach provide high levels of potassium, most sources are fairly carbohydrate heavy, such as bananas, sweet potatoes and black beans. Study subjects did consume slightly less potassium on the keto diet, but it wasn’t enough to register as statistically significant. They still exceeded the daily recommended allowance.
Supplements of both of these minerals are very popular in the keto community, and are recommended as a first line of defense against “keto flu” and muscle cramps. These athletes, who ate enough and reported no bouts of “keto flu,” didn’t seem to need any supplementation.
Still, the researchers made sure to emphasize that “appropriate sodium, potassium and magnesium intakes are necessary to achieve water balance and maintain nerve and muscle function, and vital in endurance athletes when electrolyte balance is threatened due to sweating.” Something to keep an eye on.
Iron & Copper
Consumption of both of these minerals declined in the keto diet, down to very near the recommended daily level. The researchers considered this mildly concerning. According to hemoglobin counts, the athletes were actually borderline anemic. At the same time, an actual count of iron stores in the blood showed no deficiency, prompting the authors to wonder if a ketogenic diet improves iron bioavailability.
The prescription? The authors theorized that had the participants done a better job of consuming “organ meat, nuts, soy-products, beans and sea-food,” they may have increased their intake of these minerals to safer levels without need for supplementation.
Vitamin C
Vitamin C intake declined to just barely below the recommended daily allowance. Should we be concerned? The authors of the paper don’t mention it as an issue. Banish from your mind the image of sailors contracting scurvy due to acute Vitamin C deficiency: our study volunteers consumed nearly 10 times as much Vitamin C as one would need to ward off that disease. Nevertheless, the National Institute of Health does note that “food faddists” may be in danger of Vitamin C inadequacy, a less critical condition that may have some minor deleterious effects on health. You can find plenty of Vitamin C in slightly-carby veggies such as red peppers, broccoli and cauliflower.
Thiamin
Thiamin, aka Vitamin B1, declined. It did remain above recommended dietary allowances, and the authors even speculated that in the context of a low-carb diet the body would require less thiamin. It’s worth noting that some studies have found that people with diabetes are likely to have less thiamin in their bloodstream, although none have yet identified any negative consequences. Overall, it’s not a common concern. Curious about good low-carb sources of thiamin? Choose pork and seafood.
IMPROVEMENTS
While this article focuses on nutritional deficits, let’s take a moment to celebrate the plusses that our ketogenic athletes experienced.
Omega-6 to Omega-3 Fatty Acids Ratio
Doctors agree: we all should be eating fewer omega-6’s (found most famously in vegetable oils) and more omega-3’s (found most famously in seafood). We may have evolved to eat just as many omega-3’s as omega-6’s, but the Western diet today is badly unbalanced. The average person may consume as much as 15-17 times as much omega-6 fatty acid as he or she does omega-3. This imbalance is associated with a long list of negative health outcomes.
Not a problem for the ketogenic diet: participants dropped their omega-6:omega-3 ratio by 73%, from 10:1 all the way down to 2.7:1, into a far more desirable range.
Lots of Vitamins & Minerals
Surprise, surprise. The keto eaters experienced dramatic increases in their consumption of Riboflavin, Selenium, Biotin, Vitamins A, D, E, K1, and B12.
Perhaps the most impressive change was in Vitamin D intake. Participants on the keto diet saw their dietary intake increase from 2.6 micrograms to 17.6 micrograms per day. A huge percentage of the Western world is considered to get “insufficient” amounts of Vitamin D, and supplementation is often advised. Not a problem, apparently, for the keto athletes. Moreover, Vitamin D is linked with some issues of special concern to people with diabetes, such as insulin sensitivity.
BY THE WAY, HOW DID THE HIGH-CARB GROUP DO?
I mentioned above that the researchers tested a low-carb group and a high-carb group. How did the high-carbers do?
Not so hot. Omega-6:Omega-3 fatty acids ratio increased, and Vitamins A, D, E and B12 dipped worryingly low. While the study was meant primarily to look at the ketogenic athletes, almost all of the authors’ recommendations end up focusing on the high-carb group. The authors concluded that a high-carb diet, which was based on mainstream recommendations for endurance athletes, contains too little fat and too few nutrients. High-carb athletes should eat fewer “pastas, breads and cereals” and add more fruits and leafy green vegetables.
I have been eating a well balanced ADA diet for the past 41 years as a type1, and have perfect health and zero complications