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The Ketogenic Diet for Weight Loss - Reviewed by a Registered Dietitian

Updated: Aug 30, 2020

The most-googled diet of 2018 was the “Keto” or “Ketogenic” diet, often promoted as a way to lose weight, boost health and even cure disease (1). In 2020 it's still hugely popular with “keto” recipes being the second most googled recipe type in Ireland over the last year (2).

Is this surprising? No not really, its easily one of the first diets I'm asked about when someone realises I'm a dietitian and a diet I regularly see being promoted online.

So why has this diet grabbed so much attention? Let's have a look at the science behind it, then we can make an informed choice regarding whether or not we want to embark on this very large lifestyle change.

To start and to a lot of people's surprise the ketogenic diet is actually a medical diet. It has an established medical use and is prescribed for children with epilepsy who don't tolerate or respond to medication (under the supervision of a doctor or dietitian). The evidence for the use of the ketogenic diet in adults with epilepsy remains uncertain, but is a valid option under supervision from a medical team (3).

However more recently it has become a popular diet in the media as a method for "quick fat-burning" and weight loss.

The Diet Itself:

  • It's a low-carbohydrate, moderate protein, and high fat diet. There are various versions but all usually require people to consume less than 20-50 grams of carbohydrates per day, replacing the carbohydrates removed from the diet with fat. (keep in mind the recommended daily carbohydrate intake for an average adult woman is about 250g per day) (4).

  • A typical "low carb" diet usually still contains some but not many servings of carbohydrates. To be 100% clear a keto diet is not simply "low-carb"- it's a step further. For the most part it involves cutting out all grains, bread, rice, beans, potatoes, sweets, milk, cereals, and fruits.

  • It includes lots of meat, fish, butter eggs, cheese, cream, oils, nuts, avocados, seeds and some low-carb green vegetables.

  • It is not a nutritionally complete diet meaning it requires supplementation.

  • It's also a rather expensive diet to follow.


Carbohydrate (glucose) is the main source of energy for our bodies. When our body doesn’t get enough glucose (either because we’re eliminating carbohydrates OR we haven’t eaten in a very long time), our body kind of freaks out and looks for other forms of energy to satisfy that role. Our bodies are then forced into "ketosis"; a metabolic state where you burn fat as your main source of fuel.

To be 100% clear - getting people into ketosis is not an easy process, and keeping them there is often a challenge requiring long-term support from a team of healthcare professionals.

Ketosis can be easily switched off by the body if even a few grams of extra carbohydrate are eaten.

Achieving "ketosis" is a very delicate balance. It involves:

  • Counting out grams of carbohydrates, proteins and fats.

  • Manipulating the diet to ensure that the daily food intake contains exactly the right percentage of each.

  • If weight loss is desired ensuring that there is a calorie deficit to facilitate this and this is maintained for a period of time.

  • Buying expensive ketone strips to ensure that you are truly in ketosis.

All of this may be difficult to do while trying to live your life and it is guaranteed to take a lot of time, money, dedication and hits on your social life.

The Evidence Behind the Ketogenic Diet:

The Ketogenic diet is most commonly promoted in the media to aid with weight loss, more so than other weight loss diets. The evidence for this is mixed, but studies tend to show fairly similar weight loss in comparison to other diets (5).

A recent well-conducted randomised controlled trial also showed that it may be an effective way for some people to manage type 2 diabetes (6). However it must be noted that it is an extremely difficult diet to stick to.

This brings me to the DIETFITS study. This year long study with 600+ participants highlighted that for those who are trying to lose weight, reducing calories in a realistic way is more important than whether the diet is low-carbohydrate or low-fat (7). Basically the best diet for you is the one you can stick to which brings me to my next point…

The Ketogenic Diet in "Real Life" terms:

  1. This diet is exceptionally hard to follow and even in study situations with lots of support people find it extremely difficult to stick to. In other words, people go on it and then come off it pretty quick.

  2. People attempting to follow this diet often report feeling cranky & fatigued when they cut out carbs- especially at the beginning when your body is just not accustomed to using ketone bodies as energy.

  3. As mentioned, it is very difficult to keep the body in ketosis. For example, eating just a few extra green veg, one slice of bread or a banana would take most people out of ketosis.

  4. Smell; people often report bad breath when in ketosis. This is caused by elevated ketone levels. The specific culprit is acetone, a ketone that exits the body in your urine and breath

  5. The reason why you might lose weight really quickly on the keto diet is because glycogen (our carbohydrate store in our body) is bound up in water. When you lose your glycogen stores because your not eating any carbs you tend to just drop a lot of water weight (this is not true weight/fat loss).


There are many risks with this diet including low blood sugar, metabolic derangement, vitamin and mineral deficiency, stunted growth in children, heart abnormalities and gut problems like constipation.

The health effects of following this diet in the long-term are also unknown.

There is also a potential loss of muscle mass-which we know is important for our metabolism in the long run. A lot of people think that big muscles are the result of lots of protein and protein alone- but that is just not true. When you eat carbohydrates you get an insulin response and insulin is kind of like the key to helping that protein get into the muscles to help our muscles grow (no carbohydrate, no insulin response and NO muscle growth).

Also carbs give you that quick little bout of energy so you can push it in the gym - so you might just find its harder to work out when your on the keto diet.

Finally the keto diet may encourage disordered eating behaviours; e.g. restricting, counting and obsessing over food. This can lead to anxiety in social situations that involve food. Food should add to our life not control it.

Bottom Line:

This is an extremely restrictive diet and therefore very difficult to stick to. For some specific medical conditions (like epilepsy in children) it may be worth the risk but it is strongly advised that people do not follow a diet like this without medical supervision.

There is much more evidence to support the benefits of a varied and balanced diet consisting of all of the food groups.

Everything especially carbohydrates can be enjoyed in moderation and the best diet for you is a diet that you find pleasurable that also meets your nutritional needs.

Talk to your doctor or dietitian before starting any kind of diet- but especially an extreme one like this one.



1: (accessed Aug 2020)

2: (accessed Aug 2020)

3: Martin-McGill  KJ, Bresnahan  R, Levy  RG, Cooper  PN. Ketogenic diets for drug‐resistant epilepsy. Cochrane Database of Systematic Reviews 2020, Issue 6. Art. No.: CD001903. DOI: 10.1002/14651858.CD001903.pub5.

4: European Food Safety Authority (EFSA). Dietary Reference Values for nutrients Summary report. Updated Sept 2019. (accessed Aug 2020)

5: Hall KD, Guo J. Obesity Energetics: Body Weight Regulation and the Effects of Diet Composition. Gastroenterology. 2017;152(7):1718-1727.e3. doi:10.1053/j.gastro.2017.01.052 Available from:

6: Hallberg SJ, McKenzie AL, Williams PT, et al. Effectiveness and Safety of a Novel Care Model for the Management of Type 2 Diabetes at 1 Year: An Open-Label, Non-Randomized, Controlled Study. Diabetes Ther. 2018;9(2):583-612. doi:10.1007/s13300-018-0373-9 Available from

7: Gardner CD, Trepanowski JF, Del Gobbo LC, Hauser ME, Rigdon J, Ioannidis JPA, et al. Effect of Low-Fat vs Low Carbohydrate Diet on 12-Month Weight Loss in Overweight Adults and the Association With Genotype Pattern or Insulin Secretion. JAMA [Internet]. 2018 Feb 20 [cited Aug 2020];319(7):667. Available from:

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