Missing Out on the Keto Craze?

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Should you hop on the bandwagon?

One of the latest diet trends is the “keto” (ketogenic) diet, which has eclipsed Paleo as the hottest diet trend around. Keto diets are touted as helping you lose weight, improve your memory, and live longer. And a slew of businesses are lining up to capitalize on the keto craze.

Keto dieters drastically reduce their carbohydrate intake, and replace these carbohydrates with fats.^[1] Within a few days, the body adapts to the carbohydrate shortage by burning fatty acids and producing ketone bodies, which are byproducts of metabolism that serve as an alternative energy source for the heart, brain and muscles.^[2] Since ketone production (“ketosis”) only occurs if carbohydrate intake is slim to none (no pun intended), keto diets must have very low levels of carbohydrates (less than 5% of calories).^[3],[4] The remainder of the keto diet comprises fat (75-90% of calories) and protein (5-20% of calories).^[1],[5] Thus keto diets are often referred to as “very low carbohydrate, high-fat diets” (VLCHF).

The Atkins diet, which has been around since the 1970s, was one of the first ketogenic diets to be popularized for weight loss. It starts with a VLCHF diet but then transitions to higher levels of carbs (5-15% of calories) and protein (20-30% of calories) over time, which improves compliance. Additionally, such a diet may better ensure that nutritional needs are met, which we will delve into shortly.

There’s no question that keto diets can boost weight loss, at least over the short term, but there are concerns about the long-term health consequences of such diets. Let’s take a closer look at the evidence.

Can you lose weight on a keto diet?

Weight loss can be achieved either with a VLCHF diet, which focuses on ketosis without counting calories, or with a low-calorie diet. So which approach works better?

A systematic review of 13 studies, published in 2013, reported that people who consumed VLCHF diets achieved greater weight loss than those assigned to low-calorie, low-fat diets.^[6] However, there was only a 20% difference in average weight loss on the two diets after a year. The authors state that “the differences appear to be of little clinical significance.” According to the latest scientific consensus, VLCHF diets are not superior to other dietary approaches for weight loss.^[7],[8]

In diabetic and pre-diabetic individuals, keto diets are thought to improve insulin sensitivity by lowering blood glucose and insulin levels.^[9] Some studies report significant benefits of a keto diet versus more moderate, calorie-restricted diets,^[10] while others have observed that any effects of a keto diet diminish over time.^[11],[12] A systematic review of eight randomized controlled trials concluded that “Low carbohydrate diets [which included but were not limited to the ketogenic diet] in people with type 2 diabetes were effective for short-term improvements in glycemic control, weight loss, and cardiovascular risk, but this was not sustained over the longer term.”^[13]

Most people can only sustain a very low carbohydrate diet for a few weeks or months, which explains why keto diets do not work better than other diets over the long term.

Most people can only sustain a very low carbohydrate diet for a few weeks or months, which explains why keto diets do not work better than other diets over the long term.^{[11],[14],[15]} As one group of clinicians explains, “In our experience, people are initially thrilled with the weight loss and the excellent diabetes control they get, after using keto diets. Slowly, however, they get bored with the diet. Furthermore, many feel weak and frustrated and start increasing the carbohydrate intake, and soon they are back to their original weight and diabetes control.”^[15]

A closer look at the evidence shows that a short-term keto diet may actually produce better results over the long term. This was demonstrated in a study that compared an Atkins-like diet (which began with a 2-month ketogenic phase, followed by a loosening of carbohydrate restrictions) with either a reduced-calorie Mediterranean diet or low-fat diet.^[16] Individuals on the Atkins-like plan lost weight twice as fast as those on the other diets, but the Atkins group also rebounded more quickly. Those on the Mediterranean diet lost weight more slowly, but kept it off. The average weight losses after two years were -3.3 kg on the low-fat diet, −4.6 kg on the Mediterranean diet, and −5.5 kg on the Atkins-like diet.

The use of a Mediterranean diet in the post-weight-loss phase was especially important for keeping the weight off for at least one year.

Finally, a hybrid (“biphasic”) strategy has been proposed, which starts with a keto diet for 20 days, then transitions to a low-carb non-ketogenic diet for 20 days, and then to a Mediterranean diet for four to six months.^[17] After two cycles, the results were impressive: the majority of obese participants lost weight, going from an average of 100 kg at the beginning of the study to 84 kg after 12 months. Levels of cholesterol, triglycerides, and blood glucose improved, as might be expected with a dramatic weight loss. The use of a Mediterranean diet in the post-weight-loss phase was especially important for keeping the weight off for at least one year.

Regardless of the diet’s duration, diabetic patients should be under strict medical supervision because keto diets can lower blood glucose levels and change the response to medications.

Are keto diets good for your heart?

Whether keto diets can improve heart health is debatable. A meta-analysis of 13 randomized controlled trials suggests that keto diets produce greater reductions in some cardiovascular risk factors, including triglycerides and blood pressure, than low-fat, low-calorie diets.^[6] At the same time, some of the studies showed an increase in low-density lipoprotein (LDL) cholesterol, which is associated with an increased risk of heart disease. This concern was noted in a systematic review of low-carb diets (defined as diets in which carbs comprised less than 20% of calories):^[18] “Our findings suggest that the beneficial changes of low carbohydrate diets must be weighed against the possible detrimental effects of increased LDL cholesterol,” state the authors, who caution against routinely recommending a low-carb diet to the general public.^[19]

Interestingly, in the previously mentioned Atkins-like diet study, which limited the ketogenic phase to two months, LDL cholesterol levels did not rise.^[16] Blood triglycerides declined, as did the ratio of total cholesterol to HDL cholesterol, suggesting that a short-term keto diet is more heart healthy than this diet over the long term.

Do keto diets improve brain function?

Ketogenic diets were first developed in the 1920s to help reduce seizures in children with epilepsy,^[20] a use that continues today, although the mechanism of the effect is not totally understood.^[21] Because of the positive effects seen with epilepsy, ketogenic diets are now being tested in individuals with Alzheimer’s disease (AD) and Parkinson’s disease.^[22]

In AD, the rationale behind using a keto diet is that glucose metabolism is lower in certain brain regions, and this is thought to precede and contribute to the development of AD.^[23] Since ketones provide an alternative energy source, ketosis might help preserve brain function. Pilot studies with medium-chain triglyceride (MCT) formulas, which produce ketosis without the need for a low-carb diet,^[22],[24] suggest that MCT supplementation may improve memory in some but not all AD cases.^{[25],[26],[27]} Further trials are underway to see if VLCHF ketogenic diets have the same effects as MCTs.^[22],[28]

Can a keto diet help you live longer?

Mortality went up as carbohydrate intakes went down, particularly if dietary carbs were replaced with animal fats and proteins.

Can a keto diet really help you live longer, as advertised? For mice, the answer is yes.^[29] However, this may not hold true in people. In a study encompassing more than 447,000 people around the globe, researchers at Brigham and Women’s Hospital (Boston) observed that moderate carbohydrate intakes (50-55% of calories) were associated with the lowest mortality.^[30] Mortality went up as carbohydrate intakes went down, particularly if dietary carbs were replaced with animal fats and proteins. Low-carbohydrate diets with high levels of animal fats and proteins may also increase the risk of type 2 diabetes.^[31] This is a red flag, because keto diets often rely heavily on animal foods to provide the levels of fat and protein that the diet recommends.

The low intake of a broad spectrum of nutrients as well as fiber when one follows a VLCHF diet may compromise long-term health. Dietary quality comparison of a range of popular weight loss diets has shown that low-carb diets had the poorest scores (worst quality).^[32],[33] In addition to fiber, specific nutrients of concern include thiamine, folate, magnesium, calcium, iron, and iodine, all of which have been shown to decline on keto diets.^[34] In fact, strict keto diets do not meet the established Dietary Reference Intakes (DRI) for the majority of micronutrients.^[35]

Importantly, keto diets may not provide enough dietary fiber to support good health.^{[36],[37],[38]} Population studies show that fiber deficiency increases mortality from cardiovascular, infectious, and respiratory diseases, diabetes and cancer, and all non-cardiovascular, non-cancer causes for that matter.^[39] Nutritionists and health authorities recommend at least 25 grams of dietary fiber daily for women and 38 grams per day for men,^[40] but a prototypical keto diet used in one study provided only 13 grams of fiber per day.^[36]

Consistent with insufficient dietary fiber, keto diets may alter the gut microbiota and increase the abundance of Desulfovibrio, a bacterium implicated in gut inflammation.^[41] A reduction in butyrate, a short-chain fatty acid strongly associated with gut health, and in bifidobacteria, which are beneficial for the gut and overall health, have also been seen after only eight weeks.^[36] Based on these data, the authors advised that the long-term consumption of a low carbohydrate diet may increase the risk of gastrointestinal disorders.

What’s the bottom line?

Keto diets have been hyped as solving many health problems, but the results of research paint a different picture. Such diets may boost short-term weight loss but they are not sustainable over the long term. There is a significant risk of low fiber and micronutrient intakes when consuming a VLCHF diet. Thus keto diets should only be used for short periods of time, followed by a transition to a healthier, Mediterranean-type diet. Keto followers may wish to consider multivitamin and mineral supplementation to improve nutrient status, along with fiber, probiotic, and prebiotic supplementation to help support the gut microbiota.^[42]

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