The Keto Diet: Ketogenic Diet Review & What the Research ACTUALLY Says

Should you “go keto”? What are the benefits? Is it good for weight loss? Breaking it down in this ketogenic diet review.

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The ketogenic diet has become increasingly popular. Devotees claim anything from extreme weight loss (like this PopSugar story) and increased body leanness, to improved mental stability and improved blood sugar. Well… is it true? Can you really lose loads of weight by eating heaps of bacon, cheese and MCT-oil infused coffee? Let’s dive in.

Ketogenic Diet Review

What is the ketogenic diet?

The ketogenic diet is a very low carbohydrate (usually ≤20-50 net grams carb per day), very high fat diet (80-90% of total calories), with moderate protein (~1 g per kilogram body weight), that results in ketosis. Basically this translates to a lot of meat, heavy cream, cheese, butter, oils, and some very low carbohydrate, non-starchy vegetables (e.g. bok choy, cucumber, lettuce, zucchini, peppers, cauliflower, and just a few others). Breads, pastas, fruit, beans, legumes, milk or yogurt and most other vegetables are are off-limits.

Historically, the ketogenic diet has been used in intractable seizure or epilepsy (AKA seizures that don’t respond to medication), especially in kids but also more recently in adults (1, 2). In the mainstream world, the ketogenic diet has picked up steam as a new health beacon, especially for weight loss.

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What does ketosis mean? 

Carbohydrate, or glucose, is your body’s favorite source of fuel. When the body’s in a state of ketosis, it has switched from using glucose as the primary fuel source to using fat as the primary fuel source. This only happens during periods of severe calorie restriction (including, but not only in, starvation) or severe carb restriction. During this process, the body will produce ketones. You can test whether or not your body is in ketosis with urine sampling – there will be ketones in the urine. Every body is different, so the exact amount of net g carbohydrate that must be restricted for ketosis to occur isn’t totally set in stone. It usually takes one to three days to get into ketosis. Most people reach ketosis when carbs are kept somewhere between 20 and 50 g net carb per day or less.

Is the ketogenic diet good for weight loss?

Possibly. Notably, a lot of studies evaluating the ketogenic diet for weight loss are also usually restricted in calories. With or without calorie restriction, a ketogenic diet will result in weight loss particularly at the very beginning of the diet (explained in the next section!).

Two short-term, ad libitum ketogenic studies (meaning participants could eat as much as they wanted) showed weight loss. The first I found particularly interesting because most of these studies are in obese subjects, but this was primarily in normal weight participants. In this six-week trial (n=42) of healthy individuals with an average 23.9 BMI (normal weight), participants lost an average of 2 kgs (3). They also saw a decline in physical/athletic performance. A separate, 4 week (n=17) study in obese men found that the ketogenic diet group voluntary ate less calories and felt less hungry than the moderate carbohydrate, non-ketogenic group (4). Both groups lost significant body weight, though the ketogenic diet group lost significantly more weight than the moderate carbohydrate group (4). There were no significant differences in waist circumference between groups. Both of these studies suggest successful short-term weight loss with a keto diet.

In a meta-analysis of 13 randomized-controlled trials, participants on a ketogenic diet lost significantly more weight than non-ketogenic diet participants (5). Notably if you look at the actual data, five of those thirteen did favor a low-fat diet.

A separate review found that in long-term studies, low-fat diets and ketogenic diets have similar weight loss results at 12 months (6).

Something that makes interpreting results difficult is identifying whether or not something that might be statistically significant is clinically significant. It’s noteworthy that overall in the studies I looked at (including the ones I don’t explicitly highlight here), both diet intervention groups would lose weight, but the keto group might have lost statistically significantly more. Overall, we don’t have a ton of data on the keto diet for a period greater than 12 months.

How does the ketogenic diet cause weight loss?

Right Away: At the beginning of a ketogenic diet, immediate weight loss is caused by ketonuria and depletion of glycogen stores which causes super quick loss of water weight (sorry, you didn’t just get shredded overnight!). Glycogen is the storage form of glucose, or carbohydrate. Each gram of glycogen is attached to about 2 g of water, and your body has about 100 g of glycogen stored in the liver and another 400 g in muscle (6). So, depletion of glycogen stores = loss of water weight right away.

Long-Term: There are a couple hypotheses for why keto works for weight loss in the long run. First, caloric restriction. Because the ketogenic diet is super high in fat (80-90% of total calories from fat is CRAZY high), it’s not super palatable which could cause an overall voluntary decreased intake of calories. Plus, as mentioned earlier, most of these weight loss studies are not ad libitum and the participants still have to follow a restricted calorie diet. Calorie deficit = weight loss. Second, it has been proposed that a ketogenic diet could result in decreased appetite. However, this study suggests an increased appetite at about 5% total weight loss, and no changes thereafter (7).

Is a ketogenic diet bad for your heart?

There’s not a ton of long-term data, and some is inconsistent, but overall it’s not too bad from what we know with the exception of raising LDL (“bad”) cholesterol. Interestingly, this meta-analysis found significantly greater reduction in triacylglycerides and significantly higher HDL (that’s the “good” cholesterol) levels compared to those on a low-fat diet (5).  LDL levels were significantly higher (not a good thing) in the ketogenic diet group. Diastolic blood pressure was more significantly reduced in the ketogenic diet group, with systolic blood pressure showing no significant differences. Notably, only 4 studies followed up at 24 months and at the 24-month follow-up, the only remaining statistically significant difference between the groups was HDL level. Likewise, another review found better blood lipid markers in ketogenic diets versus low-fat diets with the exception of elevated LDL cholesterol (6).

Short-term studies find slightly different results, with both LDL and total cholesterol raising within 4 to 6 weeks. In a 4-week ad lib diet of obese men, total and LDL cholesterol were more significantly reduced in the moderate carbohydrate diet group versus the ketogenic diet group, and there were no differences in blood pressure, HDL or triacylglycerol between groups (4). In a 6-week ad lib diet in normal weight, healthy adults, total and LDL cholesterol went up significantly (4.7% and 10.7%, respectively) (3).

Overall, blood lipid markers don’t show flying colors across the board for the keto diet, though some markers do improve.

Is a ketogenic diet good for type 2 diabetes?

Possibly. One study (n=89) evaluating a very low calorie ketogenic diet versus a hypocaloric diet in those with diabetes found that the keto group lost significantly more weight, more inches at the waist, had more improved fasting blood sugars, and more reduced hemoglobin A1c (HbA1c) (8). A separate, 24-week study (n=102) evaluating the same again found that in those with diabetes, the ketogenic group lost significantly more weight, had greater loss of waist circumference, and greater reduction in HbA1c than the hypocaloric diet group (9).

Keep in mind, ketosis is not the same as diabetic ketoacidosis which can be life threatening and requires immediate hospitalization.

What are the side effects of a ketogenic diet?

Some commonly cited side effects of a ketogenic diet are constipation, headache, vomiting, dizziness, fatigue or general weakness, muscle cramps, diarrhea, rash, and bad breath (3,6,7). Some of these side effects tend to be more pronounced in the first week and then taper off.

Any problems with a ketogenic diet?

Nutritionally, a ketogenic diet can be markedly low in fiber and a number of vitamins and minerals, since whole grains, legumes, fruit and a number of vegetables are off-limits due to their carb content. It would be recommended to take a multivitamin with minerals and a calcium with vitamin D supplement (10). Behaviorally, long-term compliance tends to be a problem. In one meta-analysis, six month studies displayed more impressive results than 12 month studies, possibly related to the fact that carb intake was higher than what was technically allowed by the study protocol (5).

Is the ketogenic diet safe?

If you are otherwise healthy, preliminary research suggests it may not be particularly harmful. That said, we don’t really have data on long-term effects.

Bottom line – would you recommend it?

Eh, personally… I would say we don’t have enough long-term data on later cardiovascular implications that I feel comfortable recommending a ketogenic diet for weight loss or for diabetic treatment (though reduced or controlled carbohydrate I agree with). As someone who used to cover both the surgical telemetry and neuro floors… I’ve seen the consequences of too many heart attacks and strokes to feel comfortable extrapolating data from short-term studies to long-term cardiovascular health. Secondly, I worry about other possible nutrient deficits and inadequate fiber intake. Third, it’s quite a difficult diet to sustain, and my personal philosophy is to find a dietary pattern that works long-term for my clients. That said, I can’t say it would definitely be harmful to do it.

What if I really want to do it?

If you are someone who wants to give the ketogenic diet a go, definitely consult with your doctor first and plan on close follow-up with your physician and a Registered Dietitian Nutritionist. Keep in mind if you have significant weight loss and have been on medications, it’s likely you will need your medications adjusted so very close observance would be of utmost importance. Please, do not fly by the seat of your pants on this one, especially if you have pre-existing medical conditions.

Aside from the possible clinical implications, I would really dig deep and ask yourself if you feel like that strict of a diet regimen seems realistic for your lifestyle. A serving of blueberries could kick you out of ketosis in a snap, so keep in mind there isn’t wiggle room in terms of maintaining compliance.

Disclosures: None. This blog post was not created in partnership with any brand or product. Opinions on this blog should not be taken as medical advice.

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