Are Keto Diets Safe?

Are Keto Diets Safe?
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The effects of ketogenic diets on nutrient sufficiency, gut flora, and heart disease risk.

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Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

Given the decades of use of ketogenic diets to treat certain cases of pediatric epilepsy, a body of safety data has accumulated. Nutrient deficiencies would seem to be the obvious issue. Inadequate intake of 17 micronutrients—vitamins and minerals—has been documented in those on strict ketogenic diets.

Dieting is a particularly important time to make sure you’re meeting all your essential nutrient requirements, since you may be taking in less food. Ketogenic diets tend to be so ally vacuous that one assessment estimated that to get a sufficient daily intake of all essential vitamins and minerals. you’d have to eat more than 37,000 calories a day.

That’s one of the advantages of more plant-based approaches. As the editor-in-chief of the Journal of the American Dietetic Association put it: “What could be more nutrient dense than a vegetarian diet?” Choosing a healthy diet may be easier than sticking 50 sticks of butter in your coffee.

And we’re not talking about just not reaching your daily allowances. Children have gotten scurvy on ketogenic diets, and some have even died from selenium deficiency (which can cause sudden cardiac death). The vitamin and mineral deficiencies can be solved with supplements, but what about the paucity of prebiotics, the dozens of types of fiber and resistant starches found concentrated in whole grains and beans that you’d be missing out on?

Not surprisingly, constipation is very common on keto diets, but as I reviewed before, starving our microbial self of prebiotics can have a whole array of negative consequences. Ketogenic diets have been shown to reduce the richness and diversity of our gut flora. Microbiome changes can be detected “within 24 hours” of switching to a high-fat, low-fiber diet. The lack of fiber starves our good gut bacteria, but we used to think dietary fat itself was nearly all absorbed in the small intestine. But based on studies using radioactive tracers, we now know that about 7 percent of the saturated fat in a fat-rich meal can make it down to the colon, which may result in detrimental changes in our gut microbiome, weight gain, increased leaky gut, and pro-inflammatory changes. For example, a drop in beneficial bifidobacteria and a decrease in overall short-chain fatty acid production—both of which would be expected to “increase the risk of…gastrointestinal disorders.”

Okay, but striking at the heart of the matter, what might all that saturated fat be doing to our heart? If you look at low-carbohydrate diets and all-cause mortality, those who eat lower-carb diets suffer “a significantly higher risk of all-cause mortality,” meaning they live, on average, significantly shorter lives. From a heart disease perspective, though, it matters if it’s an animal fat or plant fat. Based on the famous Harvard cohorts, eating more of an animal-based low-carb diet was associated with higher death rates from cardiovascular disease—a 50 percent higher risk of dying from a heart attack or stroke—but no such association was found for lower-carb diets based on plant sources.

And it wasn’t just from Harvard. “Low carbohydrate dietary patterns favouring animal…protein and fat, from sources such as [red meat and chicken], were associated with higher mortality; whereas those [favoring] plant protein…and fat…, [from things like] vegetables, nuts, peanut butter, and whole grain[s], were associated with lower mortality…”

Cholesterol production in the body is directly correlated to body weight.  Every pound of weight loss by nearly any means is associated with about a one-point drop in cholesterol levels in the blood. But put people on very low-carb ketogenic diets and the beneficial effect on LDL bad cholesterol is blunted or even completely neutralized. Counterbalancing changes in LDL size or HDL (what we used to think of as good cholesterol) are not considered sufficient to offset this risk. You don’t have to wait until cholesterol builds up in your arteries to have adverse effects, though. Within three hours of eating a meal high in saturated fat, you can see a significant impairment of artery function. Even with a dozen pounds of weight loss, artery function worsens on a ketogenic diet instead of getting better—which appears to be the case with low-carb diets in general.

So: bad for the gut, bad for the heart, but is it bad to the bone? We’ll find out next.

Please consider volunteering to help out on the site.

  • Zupec-kania B, Zupanc ML. Long-term management of the ketogenic diet: seizure monitoring, , and supplementation. Epilepsia. 2008;49 Suppl 8:23-6.
  • Calton JB. Prevalence of micronutrient deficiency in popular diet plans. J Int Soc Sports Nutr. 2010;7:24.
  • Farmer B, Larson BT, Fulgoni VL, Rainville AJ, Liepa GU. A vegetarian dietary pattern as a nutrient-dense approach to weight management: an analysis of the national health and examination survey 1999-2004. J Am Diet Assoc. 2011;111(6):819-27.
  • Willmott NS, Bryan RA. Case report: scurvy in an epileptic child on a ketogenic diet with oral complications. Eur Arch Paediatr Dent. 2008;9(3):148-52.
  • Bank IM, Shemie SD, Rosenblatt B, Bernard C, Mackie AS. Sudden cardiac death in association with the ketogenic diet. Pediatr Neurol. 2008;39(6):429-31.
  • Office of Nutrition and Food Labeling, Center for Food Safety and Applied Nutrition, Food and Drug Administration. Science Review of Isolated and Synthetic Non-Digestible Carbohydrates. 2016.
  • Wibisono C, Rowe N, Beavis E, et al. Ten-year single-center experience of the ketogenic diet: factors influencing efficacy, tolerability, and compliance. J Pediatr. 2015;166(4):1030-6.e1.
  • Zhang Y, Zhou S, Zhou Y, Yu L, Zhang L, Wang Y. Altered gut microbiome composition in children with refractory epilepsy after ketogenic diet. Epilepsy Res. 2018;145:163-168.
  • Wu GD, Chen J, Hoffmann C, et al. Linking long-term dietary patterns with gut microbial enterotypes. Science. 2011;334(6052):105-8.
  • Gabert L, Vors C, Louche-pélissier C, et al. 13C tracer recovery in human stools after digestion of a fat-rich meal labelled with [1,1,1-13C3]tripalmitin and [1,1,1-13C3]triolein. Rapid Commun Mass Spectrom. 2011;25(19):2697-703.
  • Cândido FG, Valente FX, Grześkowiak ŁM, Moreira APB, Rocha DMUP, Alfenas RCG. Impact of dietary fat on gut microbiota and low-grade systemic inflammation: mechanisms and clinical implications on obesity. Int J Food Sci Nutr. 2018;69(2):125-143.
  • Brinkworth GD, Noakes M, Clifton PM, Bird AR. Comparative effects of very low-carbohydrate, high-fat and high-carbohydrate, low-fat weight-loss diets on bowel habit and faecal short-chain fatty acids and bacterial populations. Br J Nutr. 2009;101(10):1493-502.
  • Noto H, Goto A, Tsujimoto T, Noda M. Low-carbohydrate diets and all-cause mortality: a systematic review and meta-analysis of observational studies. PLoS ONE. 2013;8(1):e55030.
  • Li S, Flint A, Pai JK, et al. Low carbohydrate diet from plant or animal sources and mortality among myocardial infarction survivors. J Am Heart Assoc. 2014;3(5):e001169.
  • Seidelmann SB, Claggett B, Cheng S, et al. Dietary carbohydrate intake and mortality: a prospective cohort study and meta-analysis. Lancet Public Health. 2018;3(9):e419-e428.
  • Nestel PJ, Whyte HM, Goodman DS. Distribution and turnover of cholesterol in humans. J Clin Invest. 1969;48(6):982-91.
  • Dattilo AM, Kris-etherton PM. Effects of weight reduction on blood lipids and lipoproteins: a meta-analysis. Am J Clin Nutr. 1992;56(2):320-8.
  • Bueno NB, De melo IS, De oliveira SL, Da rocha ataide T. Very-low-carbohydrate ketogenic diet v. low-fat diet for long-term weight loss: a meta-analysis of randomised controlled trials. Br J Nutr. 2013;110(7):1178-87.
  • Sacks FM, Lichtenstein AH, Wu JHY, et al. Dietary Fats and Cardiovascular Disease: A Presidential Advisory From the American Heart Association. Circulation. 2017;136(3):e1-e23.
  • Nicholls SJ, Lundman P, Harmer JA, et al. Consumption of saturated fat impairs the anti-inflammatory properties of high-density lipoproteins and endothelial function. J Am Coll Cardiol. 2006;48(4):715-20.
  • Phillips SA, Jurva JW, Syed AQ, et al. Benefit of low-fat over low-carbohydrate diet on endothelial health in obesity. Hypertension. 2008;51(2):376-82.
  • Schwingshackl L, Hoffmann G. Low-carbohydrate diets impair flow-mediated dilatation: evidence from a systematic review and meta-analysis. Br J Nutr. 2013;110(5):969-70.

Image credit: maglara via adobe stock photos. Image has been modified.

Motion graphics by Avocado Video

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

Given the decades of use of ketogenic diets to treat certain cases of pediatric epilepsy, a body of safety data has accumulated. Nutrient deficiencies would seem to be the obvious issue. Inadequate intake of 17 micronutrients—vitamins and minerals—has been documented in those on strict ketogenic diets.

Dieting is a particularly important time to make sure you’re meeting all your essential nutrient requirements, since you may be taking in less food. Ketogenic diets tend to be so ally vacuous that one assessment estimated that to get a sufficient daily intake of all essential vitamins and minerals. you’d have to eat more than 37,000 calories a day.

That’s one of the advantages of more plant-based approaches. As the editor-in-chief of the Journal of the American Dietetic Association put it: “What could be more nutrient dense than a vegetarian diet?” Choosing a healthy diet may be easier than sticking 50 sticks of butter in your coffee.

And we’re not talking about just not reaching your daily allowances. Children have gotten scurvy on ketogenic diets, and some have even died from selenium deficiency (which can cause sudden cardiac death). The vitamin and mineral deficiencies can be solved with supplements, but what about the paucity of prebiotics, the dozens of types of fiber and resistant starches found concentrated in whole grains and beans that you’d be missing out on?

Not surprisingly, constipation is very common on keto diets, but as I reviewed before, starving our microbial self of prebiotics can have a whole array of negative consequences. Ketogenic diets have been shown to reduce the richness and diversity of our gut flora. Microbiome changes can be detected “within 24 hours” of switching to a high-fat, low-fiber diet. The lack of fiber starves our good gut bacteria, but we used to think dietary fat itself was nearly all absorbed in the small intestine. But based on studies using radioactive tracers, we now know that about 7 percent of the saturated fat in a fat-rich meal can make it down to the colon, which may result in detrimental changes in our gut microbiome, weight gain, increased leaky gut, and pro-inflammatory changes. For example, a drop in beneficial bifidobacteria and a decrease in overall short-chain fatty acid production—both of which would be expected to “increase the risk of…gastrointestinal disorders.”

Okay, but striking at the heart of the matter, what might all that saturated fat be doing to our heart? If you look at low-carbohydrate diets and all-cause mortality, those who eat lower-carb diets suffer “a significantly higher risk of all-cause mortality,” meaning they live, on average, significantly shorter lives. From a heart disease perspective, though, it matters if it’s an animal fat or plant fat. Based on the famous Harvard cohorts, eating more of an animal-based low-carb diet was associated with higher death rates from cardiovascular disease—a 50 percent higher risk of dying from a heart attack or stroke—but no such association was found for lower-carb diets based on plant sources.

And it wasn’t just from Harvard. “Low carbohydrate dietary patterns favouring animal…protein and fat, from sources such as [red meat and chicken], were associated with higher mortality; whereas those [favoring] plant protein…and fat…, [from things like] vegetables, nuts, peanut butter, and whole grain[s], were associated with lower mortality…”

Cholesterol production in the body is directly correlated to body weight.  Every pound of weight loss by nearly any means is associated with about a one-point drop in cholesterol levels in the blood. But put people on very low-carb ketogenic diets and the beneficial effect on LDL bad cholesterol is blunted or even completely neutralized. Counterbalancing changes in LDL size or HDL (what we used to think of as good cholesterol) are not considered sufficient to offset this risk. You don’t have to wait until cholesterol builds up in your arteries to have adverse effects, though. Within three hours of eating a meal high in saturated fat, you can see a significant impairment of artery function. Even with a dozen pounds of weight loss, artery function worsens on a ketogenic diet instead of getting better—which appears to be the case with low-carb diets in general.

So: bad for the gut, bad for the heart, but is it bad to the bone? We’ll find out next.

Please consider volunteering to help out on the site.

  • Zupec-kania B, Zupanc ML. Long-term management of the ketogenic diet: seizure monitoring, , and supplementation. Epilepsia. 2008;49 Suppl 8:23-6.
  • Calton JB. Prevalence of micronutrient deficiency in popular diet plans. J Int Soc Sports Nutr. 2010;7:24.
  • Farmer B, Larson BT, Fulgoni VL, Rainville AJ, Liepa GU. A vegetarian dietary pattern as a nutrient-dense approach to weight management: an analysis of the national health and examination survey 1999-2004. J Am Diet Assoc. 2011;111(6):819-27.
  • Willmott NS, Bryan RA. Case report: scurvy in an epileptic child on a ketogenic diet with oral complications. Eur Arch Paediatr Dent. 2008;9(3):148-52.
  • Bank IM, Shemie SD, Rosenblatt B, Bernard C, Mackie AS. Sudden cardiac death in association with the ketogenic diet. Pediatr Neurol. 2008;39(6):429-31.
  • Office of Nutrition and Food Labeling, Center for Food Safety and Applied Nutrition, Food and Drug Administration. Science Review of Isolated and Synthetic Non-Digestible Carbohydrates. 2016.
  • Wibisono C, Rowe N, Beavis E, et al. Ten-year single-center experience of the ketogenic diet: factors influencing efficacy, tolerability, and compliance. J Pediatr. 2015;166(4):1030-6.e1.
  • Zhang Y, Zhou S, Zhou Y, Yu L, Zhang L, Wang Y. Altered gut microbiome composition in children with refractory epilepsy after ketogenic diet. Epilepsy Res. 2018;145:163-168.
  • Wu GD, Chen J, Hoffmann C, et al. Linking long-term dietary patterns with gut microbial enterotypes. Science. 2011;334(6052):105-8.
  • Gabert L, Vors C, Louche-pélissier C, et al. 13C tracer recovery in human stools after digestion of a fat-rich meal labelled with [1,1,1-13C3]tripalmitin and [1,1,1-13C3]triolein. Rapid Commun Mass Spectrom. 2011;25(19):2697-703.
  • Cândido FG, Valente FX, Grześkowiak ŁM, Moreira APB, Rocha DMUP, Alfenas RCG. Impact of dietary fat on gut microbiota and low-grade systemic inflammation: mechanisms and clinical implications on obesity. Int J Food Sci Nutr. 2018;69(2):125-143.
  • Brinkworth GD, Noakes M, Clifton PM, Bird AR. Comparative effects of very low-carbohydrate, high-fat and high-carbohydrate, low-fat weight-loss diets on bowel habit and faecal short-chain fatty acids and bacterial populations. Br J Nutr. 2009;101(10):1493-502.
  • Noto H, Goto A, Tsujimoto T, Noda M. Low-carbohydrate diets and all-cause mortality: a systematic review and meta-analysis of observational studies. PLoS ONE. 2013;8(1):e55030.
  • Li S, Flint A, Pai JK, et al. Low carbohydrate diet from plant or animal sources and mortality among myocardial infarction survivors. J Am Heart Assoc. 2014;3(5):e001169.
  • Seidelmann SB, Claggett B, Cheng S, et al. Dietary carbohydrate intake and mortality: a prospective cohort study and meta-analysis. Lancet Public Health. 2018;3(9):e419-e428.
  • Nestel PJ, Whyte HM, Goodman DS. Distribution and turnover of cholesterol in humans. J Clin Invest. 1969;48(6):982-91.
  • Dattilo AM, Kris-etherton PM. Effects of weight reduction on blood lipids and lipoproteins: a meta-analysis. Am J Clin Nutr. 1992;56(2):320-8.
  • Bueno NB, De melo IS, De oliveira SL, Da rocha ataide T. Very-low-carbohydrate ketogenic diet v. low-fat diet for long-term weight loss: a meta-analysis of randomised controlled trials. Br J Nutr. 2013;110(7):1178-87.
  • Sacks FM, Lichtenstein AH, Wu JHY, et al. Dietary Fats and Cardiovascular Disease: A Presidential Advisory From the American Heart Association. Circulation. 2017;136(3):e1-e23.
  • Nicholls SJ, Lundman P, Harmer JA, et al. Consumption of saturated fat impairs the anti-inflammatory properties of high-density lipoproteins and endothelial function. J Am Coll Cardiol. 2006;48(4):715-20.
  • Phillips SA, Jurva JW, Syed AQ, et al. Benefit of low-fat over low-carbohydrate diet on endothelial health in obesity. Hypertension. 2008;51(2):376-82.
  • Schwingshackl L, Hoffmann G. Low-carbohydrate diets impair flow-mediated dilatation: evidence from a systematic review and meta-analysis. Br J Nutr. 2013;110(5):969-70.

Image credit: maglara via adobe stock photos. Image has been modified.

Motion graphics by Avocado Video

Doctor's Note

There’s just a few videos left in my keto series. Here’s what we have so far:

And here’s what’s coming up:

The video I mentioned is Gut Dysbiosis: Starving Our Microbial Self. For more on keeping our gut bugs happy see:

What’s the best diet for our heart? Given that heart disease is the #1 killer of men and women, consider a diet centered around whole plant foods: How Not to Die from Heart Disease.

If you haven’t yet, you can to my videos for free by clicking here and to my audio podcast here ( by clicking on your mobile device’s icon). 

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