There is a lot of hype about the ketogenic (keto) diet — and I wonder — is this a fad, like most diets and doomed to fail, or is it here to stay? I was curious, so I dove into the research.
The findings I am presenting here focus on keto as a means to address weight loss only. There are other benefits keto may impart such as lowering triglyceride levels or improving the management of diabetes — to name a few — but my focus is weight loss, since this is a concern for many of my clients.
If you are pressed for time, click here for the key takeaways by topic and check out the "bottom line" for each section:
Before I get into the findings, here are some research-related considerations.
Resources: where did I find my data?
I relied on a few key sources including clinical trials, PubMed (limiting my search to reviews, meta-analyses, and systematic reviews in the past 5 years — which came out to 72 studies) and the Cochrane database.
I also just finished reading Gary Taubes’ book: The Case for Keto: Rethinking Weight Control and the Science and Practice of Low-Carb, High-Fat Eating. It includes references to research studies, but mainly focuses on results from his interviews with about 100 physicians who have recommended keto to their patients.
Study limitations and considerations
The studies tend to include small sample sizes and very few report on long-term outcomes. Since most nutrition studies rely on patient self-reporting and recall, the resulting data may not be the most reliable. Furthermore, most studies don’t include information on the quality of the foods consumed. So, the evidence should be taken with a grain of salt.
What is a keto diet?
Keto is a way of eating that includes high fat, low carbohydrate (aka carbs) and fairly low protein intake. The idea is that this way of eating will force your body into ketosis, meaning your body will use fat as fuel—and more specifically ketones—which the liver produces from stored fat, as opposed to using glucose, which is your main source of fuel that comes from carbs.
So the general nutritional breakdown of the keto diet is as follows:
At least 70-80% of calories derived from fat
About 10-20% from protein and less than 10% from carbs.
For your body to go into ketosis, an adult must stay below 50 grams of carbs each day.
This can be challenging for sure, but the good thing is that you are not bound to calorie counting and you can eat to satiety.
History of keto
Keto was used in the 19th century to treat diabetes (until the discovery of insulin), and then in the 1920’s it was primarily used to treat epilepsy in children.
In recent years, the keto diet has gained renewed attention as a solution for people struggling with their weight and diabetes, amongst a myriad of other health issues the diet may help improve.
Overall, the research on the benefits of keto is somewhat limited, however, the last few years has seen a significant increase in the studies published.
Is keto effective for weight loss and sustainable in the long-term?
According to a 2019 literature review by the National Lipid Association, there is evidence that a very low-carb diet can help you lose more weight than the standard high-carb, low-fat diet — at least for the first two to six months. In a review, Ting et al., 2018 found that at the one year period, keto diets can help patients lose about 2 kg (4.4 lbs) more than low-fat diets and that weight loss peaks at about 5 months, but is often not sustained. Effects were also found to generally not be sustained after 12 months in a review by Batch et al., 2020.
However, some studies (Moreno et al., 2014), including a meta-analysis by Bueno et al. 2013, indicate that keto diets are even effective in the longer term (about a year). A review of 12 studies found that weight loss was even stable for up to 2 years; while another by Muscogiuri et al. 2021, providing European Guidelines for Obesity Management in Adults, also found that greater weight loss was sustained on keto compared to other types of weight loss interventions at the 1 year mark.
Bottom line: In the short-term, it appears that keto does contribute to weight loss, though at times only moderately. Some studies do show that at 1 year follow-up, and even 2 year follow-up, weight loss is sustained, but these findings are not consistent.
What is the verdict on the long-term safety of keto for heart disease?
We’ve been so ingrained to believe that fat is bad for you, but fat serves many
necessary functions in the body such as supporting cell growth and helping absorb vital nutrients. The evidence has shown that trans fats are the only fats shown to have an adverse effect on heart health.
According to some practitioners and writers (Hyman 2016; Kresser; Taubes 2011), dietary fat, including saturated fat and cholesterol do not cause heart disease. These same authors have dispelled the heart diet hypothesis originally introduced by Ancel Keys, counteracting it with evidence that sugar is the real culprit.
The idea is that metabolic syndrome (a set of risk factors such as obesity, insulin resistance, high triglycerides, high blood pressure etc…) increases your risk for heart disease. According to Gary Taubes, “If you have metabolic syndrome, it’s the quantity and quality of carbohydrates you’re eating that are slowly shortening your life. Saturated fat is not responsible“.
Regardless of whether fat or sugar are the culprit, studies have shown that people on a keto diet see increases in their LDL cholesterol, as well as HDL, but tend to see decreases in their triglycerides (the latter two are a good thing!) (Bueno, 2013; O’Neill & Ragi, 2020). According to the National Lipid Association’s review, beyond a year though, it appears that these benefits don’t last. Only lowered triglyceride levels seem to have any lasting effects.
The supporters of a keto lifestyle argue that HDL and triglyceride levels are better predictors of heart disease than LDL anyway. They also contend that keto increases the number of large buoyant LDL particles, but not the more dangerous small-dense LDL particles (O’Neill & Ragi, 2020). In addition, the latter are better measures of the risk of heart disease compared to cholesterol levels.
Check out any of the above-mentioned authors for more details and a wealth of evidence on the topic of fat that I’ve attempted to summarize in a mere paragraph which certainly does not do it justice!
Bottom line: It’s not clear yet what the long-term impact is of eating a high fat diet on heart health.
Contraindications and physician guidance regarding the keto diet
According to Steven Phinney—a long time expert on keto—getting the keto diet right is complex and needs to be done in a safe way, especially if you have underlying conditions such as heart issues, liver and kidney disease, high blood pressure or diabetes.
At this point, we do not know if keto is safe during pregnancy and breastfeeding; in childhood and the adolescent years; for higher risk individuals with multiple health conditions; or for the elderly.
We do not know for these groups whether the benefits of the diet outweigh the risks. A review by Watanabe et al., provides some guidelines on who should not be on a keto diet.
If you are even wondering whether your underlying condition might be an issue, I recommend that you consult with your physician and/or a dietitian or someone knowledgeable on this topic.
If you are exploring keto on your own, make sure you listen to what your body is telling you. If you experience any changes that are unpleasant, your body is telling you to back off so please listen carefully!
Bottom line: If you have any underlying conditions, please make sure you consult with a physician or someone knowledgeable about keto.
Tailoring keto to meet women's needs
Men tend to experience better success on keto than women. Some women report weight gain, cycle changes and other hormone related shifts while on keto.
If you are having a menstrual cycle, it is important that you stay in tune with your hormonal shifts and that you sync your diet with your cycle. For example, you may consider increasing your carb intake during the second half of your cycle to support progesterone production. Check out Leanne Vogel’s podcast The Keto Diet, episode #312 “Adjusting Keto for your Cycle”. This is worth a listen and is a great synthesis on how hormones can impact your success on keto.
An insightful article by Arbour et al., 2021 provides guidance for nurses (but very helpful for patients too) on how to counsel women about keto and intermittent fasting (IF) at various life stages of women’s health — pre-conception, pregnancy, breastfeeding, and perimenopause/menopause. They include a useful set of laboratory measures such as liver function tests, lipid levels and glucose to monitor while on a keto and IF regimen.
Bottom line: Be mindful of how your hormones impact how you feel on keto and be ready to modify and adjust your carb intake.
Compliance on a restrictive diet: cyclical keto
For some, compliance to such a strict diet may not be possible. A middle ground could be to adopt a cyclical keto diet where you eat carbs one to two days of the week, and then follow a standard keto diet the remaining days of the week.
Or you can implement a modified carb diet where you are really paying attention to the quality (for example eating whole grains instead of white bread) and quantity of the carbs you are eating.
And what about eating all those animal products? Some may have ethical issues around that and I get it. I feel the same! Know that it is possible to do a keto diet by incorporating vegetarian or vegan options such tofu, tempeh, nut butters, nuts and avocado.
Bottom line: It may be challenging to comply long-term with keto, so consider adopting a cyclical keto diet. If you are concerned about consuming so many animal products, consider reducing those products or adopting a vegetarian/vegan keto diet.
Try it out!
The best way to find out if keto works for you is to try it yourself. Regardless of what the research says, tune into how you feel when you eat this way and how your body responds.
Personally, I cannot eat that much fat because it doesn't make me feel good. So I play around with the balance of the macronutrients to find my sweet spot. There is great variation in how individuals process carbs and fats so you will need to experiment, be curious and see what works for you.
Bottom line: Honor who you are and what your body needs. Do YOU.
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