Ketogenic or “keto” diets have become one of today’s biggest trends.
Many people who adopt a keto diet do it to break cravings for sugary, starchy carbohydrates, primarily to aid weight loss.
And although it may not be their primary goal, cutting back on sugary, starchy carbs is also likely to reduce their risks for diabetes, obesity, and heart disease.
Keto diets — which originated as treatments for epilepsy — typically derive 10-20% of their calories from protein, 5-10% of calories from carbohydrates, and a whopping 70-80% of calories from fat.
In contrast, official U.S. guidelines for macronutrient intakes recommend getting 45-65 percent of daily calories from carbohydrates, 20-35 percent from fat, and 10-35 percent from protein.
Weirdly, although official guidelines emphasize getting carbs from nutritious sources — vegetables, fruits, whole grains, and beans — they only limit added sugars to a seriously unhealthful 25% of daily calories.
You can certainly eat a healthful diet based on the proportions of macronutrients recommended in official guidelines — but keto and Paleo/Atkins-style diets provide them in proportions very different from those guidelines and each other’s.
Let’s look at each of those two basic alternative approaches to diet, and then explore the pros and cons of ketogenic diets.
High-protein Paleo/Atkins diets vs. high-fat keto diets
Compared with official diet recommendations, keto-style and Paleo/Atkins-style eating plans call for getting many fewer calories from carbohydrates.
However, while Paleo/Atkins diets replace most carb calories with roughly equal proportions of calories from protein and fat, ketogenic diets replace most carbohydrate calories with calories from fat, placing much less emphasis on protein.
Because keto diets provide so few carbs, the body must instead burn dietary fat to provide most of its energy needs.
Acidic compounds called ketones get created in the liver when the body lacks carbohydrates and instead burns fat for energy. In turn, fat-burning eventually leads to the metabolic state called ketosis (ketogenic means “ketosis-creating”).
Ketones also get created when the body lacks insulin, which explains why people with diabetes — especially type 1 diabetes — can develop life-threatening ketoacidosis.
It’s interesting to note that Dr. Atkins’ original diet plan called for slashing carbohydrate intake severely during the first two weeks, in order to induce ketogenesis and help people curb their carb cravings.
So-called MCT-keto diets are sometimes prescribed for children with epilepsy, because they allow broader food choices and bigger portion sizes.
Compared with typical dietary fat, MCTs (medium-chain triglycerides) produce more ketones per calorie, thereby allowing patients to consume less total fat and more protein and carbs.
Coconut oil is the richest food source of MCTs but it still has much less than medical MCT supplements. Nonetheless, their MCT content explains why coconut oil and coconut meat are common components of popular ketogenic diets.
What does a keto diet look like?
The typical keto diet plan includes fats at every meal and fatty snacks as needed to reach about 75% of daily calories:
Ketogenic diets: The weight/metabolism upside
Preliminary clinical evidence suggested that — compared with lower-fat/higher-carb diets (Zone, LEARN, and Ornish) — keto diets can yield greater weight loss in overweight people (Noakes M et al. 2007).
Those early findings were bolstered by a review of 13 randomized controlled trials, each of which assigned overweight and obese participants to a low-fat or very-low-carb ketogenic diet and followed them for one to two years. The authors concluded that ketogenic diets shed about two more pounds while producing modestly lower triglyceride levels and blood pressure and slight rises in HDL (“good”) and LDL (“bad”) cholesterol levels (Bueno NB et al. 2013).
Importantly, the advantages seen for the ketogenic diets in that evidence review diminished after one year, probably because — due to lifelong eating habits and the body’s inherent craving for carbs — most people find it very hard to maintain a ketogenic diet.
Surprisingly, other clinical research found that overweight people on calorie-unrestricted keto diets experienced no more hunger than those following very-low-calorie diets (Gibson AA et al. 2015).
Finally, the results of a small clinical trial showed that on average, people who spent six months on a 900-calorie ketogenic diet followed by six months on an 1,800-calorie Mediterranean-style diet lost 10% of their body weight and kept it off for a full year. Those results suggest that Dr. Atkins was wise to recommend adhering to a ketogenic diet temporarily, followed by a less extreme low-carb maintenance diet (Paoli A et al. 2015).
Ketogenic diets: Long-term risk to the liver?
Medical experts haven’t been very concerned about the short-term effects of ketogenic diets, but we lack evidence about the long-term impact of being in a continuous state of ketosis.
When sustained for more than a few weeks or months, ketogenic diets could produce some health problems:
But the biggest risk posed by long-term adherence to a ketogenic diet is non-alcoholic fatty liver disease or NAFLD — a fear stimulated by the results of animal studies.
Experts now estimate that about one in three Americans has NAFLD — usually without knowing it — while rates of NAFLD have been rising here and worldwide, in parallel with rising rates of obesity and diabetes.
However, while diabetes, obesity, and heart disease are linked to high-calorie diets rich in fats and carbs, fatty ketogenic diets are very low in carbs and are not high in calories.
People with NAFLD are twice as likely to die from heart disease or stroke, while about one in five have non-alcoholic steatohepatitis or NASH. Especially in obese people and diabetics, NASH can progress to cirrhosis (scarring of the liver) or liver cancer.
Scientists also believe that, even in the absence of cirrhosis, NAFLD promotes liver cancer and — based on preliminary results from a Mayo Clinic study – other forms of cancer as well.
NAFLD is often called a “silent” killer because it typically causes no pain or other symptoms until it’s progressed to a more serious stage, like NASH or cirrhosis.
In addition to their extremely high proportion of fat, keto diets can also be high in cholesterol, depending on their sources of fat. While plant foods have no cholesterol, fatty meats can be quite high in cholesterol. (Fatty fish is not high in cholesterol.)
Why does the cholesterol content of a ketogenic diet matter, given that recent research has refuted the alleged link between dietary cholesterol and heart disease?
The concern about high-cholesterol ketogenic diets flows from the fact that animal studies find that consuming lots of fat with lots of cholesterol exerts unhealthfully synergistic effects on the immune system — effects that promote NAFLD significantly more than high-fat/normal-cholesterol diets.