What is a keto diet?
A keto diet is a type of diet where a person eats and drinks a very small amount of carbohydrates each day. Usually a keto involves eating less than 50g of carbohydrate a day but this may also be less. Some people will eat less than 20g per day.
Carbohydrates are found in starchy and sugary food such as bread, pasta, rice, cereal and also cakes, biscuits, sweets. Carbohydrates are also found in vegetables and fruit. Therefore, people following a true keto diet tend to eat small amounts of these food groups also.
Carbohydrates are converted into glucose to help provide energy for your body. Your brain and central nervous system particularly likes glucose as a fuel.
A keto diet relies more on protein based foods like meat, fish. eggs, nuts, cheese, butter and oils.
A keto diet can be used for a few iterations but the main uses are for weight loss and lowering blood glucose levels in diabetes. It is thought by eating less carbohydrates your body has to use more fat to fuel your body.
Ketones as energy
When your body breaks down fat it produces 2 sources of energy. One are called fatty acids and the other are ketones. Everyone produces some level of ketones regardless of whether you eat carbohydrates or not. However, when following a keto diet, your body increases its production of ketones to help compensate for the lack of glucose in your system.
Your body will also make some glucose from fat and protein in a process called ‘gluconeogensis’. However, ketones can also fuel the brain and the central nervous system and so less glucose is needed than if you ate carbohydrates.
When someone is following a keto diet they are said to be in ketosis. You can test this with urine sticks or blood ketone sticks. For a better understanding on ketone metabolism we’ve written a blog about this which you can find here.
Keto diet and weight loss
Keto diets have been found to be effective in weight loss. There are many people who swear by the diet and can’t recommended it enough. On the flip side, there are many people I meet in clinic who follow it and do not lose weight.
Therefore, the first thing to note is ketosis is not a one way ticket to weight loss. You still need to consume less calories than your body needs.
The research comparing different diets actually shows keto diets may be superior in at least the short term for weight loss. Most studies last only about 6 months or less and typically show keto diets help participants to lose around 5kg on average in weight. This is compared to the next closest rival, the Mediterranean diet, where people tend to lose around 4kg.
Whether this different is specifically to do with ketosis or not is up for debate. Ultimately, your body requires a certain amount of energy each day, which needs to be fuelled. Therefore, if you eat more than that requirement, the energy can’t just be evaporated and therefore will still be stored as fat.
Reasons for weight loss
In reality, the diet is likely to exert a better weight loss effect due to the rules of the diet. Starch tends to be one of the biggest contributors to peoples diet in the UK. We also massively over eat this food group. Therefore, cutting this out, reduces ones calories significantly.
The other food group that cannot be consumed on a keto diet is sugary foods. As ketosis is measured, one chocolate bar may be enough to turn off ketosis. Therefore, people following the diet can remain quite motivated to avoid such foods. So this is a good thing.
However, by completely restricting such foods, it’s likely an individual’s total calorie intake is further reduced.
As a result, it is much more likely people following this diet lose more weight because of the negative energy balance it creates as opposed to ketosis itself.
Keto diet and diabetes
Keto diets are also used regularly in the management of diabetes. From experience they are used more in type 2 diabetes than in other types.
Carbohydrates are the foods that increase blood glucose levels. Therefore, limiting the amount of carbohydrates you eat, will act to reduce your glucose levels.
Keto and type 2 diabetes
Lowering your carbohydrate intake will definitely lower your blood glucose levels. However, remember it is not the carbohydrates causing your high blood glucose levels in the first place. It is your bodies inability to deal with the carbohydrates.
Anyone without diabetes can eat carbohydrates just fine without any problems.
So what is causing the problem? Generally speaking in type 2 diabetes, it is too much fat surrounding the liver, pancreas and cells of the body. It can also be due to being unfit or inactive.
Though lowering your carbohydrate intake will help your glucose levels, it doesn’t necessarily treat the cause of the problem. Losing weight and getting active treats the underlying problem and helps to shed the fat around the organs. This helps to lower your baseline glucose level.
Keto diet and type 2 medications
It appears quite clear following a keto diet with type 2 diabetes helps to lower the amount of medications you need to take. This is particularly true of medications designed to help lower glucose levels after foods such as sulphonylureas or certain insulins.
Therefore, a keto diet likely lowers the medication burden for many people.
Of course, if you are taking insulin or sulphonylureas, speak with your medical team before starting a keto diet because there is a big risk of hypoglycaemia (low blood glucose levels).
There are some dangers though. People taking an SGLT-2 inhibitor (Canagliflozin, Dapagliflozin, Empagliflozin – anything ending in gliflozin) should not embark on a keto diet whilst taking this medication. This class of medication makes you urinate more glucose out. This can lead to dehydration. If you then become unwell and your glucose levels rise, the dehydration and stress response can push the body into a state called diabetic keto acidosis. This is can be fatal if not treated quickly.
There’s been a number of occurrences in recent times of people starting a keto diet whilst taking these medications and becoming acutely unwell.
Keto diet and type 1 diabetes
Once again, a keto diet can help to stabilise erratic glucose levels. Particularly if you’re someone who is prone to after meal spikes. However, there are also people who have excellent glucose control and eat plenty of carbohydrates.
Anecdotally, I have personally seen success using low carbohydrate diets in type 1 diabetes but rarely recommend a full keto diet.
One of the reasons for this is the risk with generating ketones. Anyone with type 1 diabetes should have been told about testing for ketones if they are unwell. However, if you are already running a base level of ketones due to the diet, it can mask any dangerous ketone formation independent of diet.
This can quickly lead to people developing diabetic keto acidosis.
The other risk with having a base level of ketones from your diet is it reduces your margin of error before dangerous ketone levels form.
Keto diet and hypos in type 1 diabetes
All patients with type 1 diabetes take insulin and insulin has the potential to push your glucose level too low. Cutting out most sources of carbohydrates in your diet will increase the chances of hypos.
Not only does it increase the chances of hypos, it also makes them more difficult to treat. Normally, when you experience a hypo your body releases glycogen from the liver to help increase your levels. With little carbohydrate in your diet, the liver, kidneys and muscles have little reserves of glucose to release. Therefore, hypos can be exacerbated by following a keto diet.
Keto diets and general health
There appears some positive outcomes when people start on a keto diet. We’ve already established keto diets can help you lose weight. If you are overweight or obese, losing weight will improve your health and lower your disease risk. So this is only a good thing.
The studies I looked at also showed favourable results for lowering blood lipids like cholesterol and triglycerides. However, this is likely related to those participants also losing weight simultaneously. It might seem like nitpicking as to why the diet exerted this laid lowering effect. However, this means the participants increased blood lipids were weight related and thus the reduction is not necessarily just keto specific. In other words, had the participants lost weight via any other means, the same effect would have been achieved.
These studies were generally short duration and so we can’t be sure of the long term effects but nonetheless, it is promising.
The cons of a keto diet look a little bit longer term. There isn’t a great deal of evidence looking at the subject but there were a few studies I found, 2 of which I wanted to discuss today.
The first study I looked at was called the ‘PURE study’. This didn’t actually look at keto diets but instead focused on the effect of high carbohydrates diets. So it looks at the opposite end of the spectrum.
This study looked at 135,000 people over 18 countries over a median time span of 7.4 years.
The duration of the study was fair but not super long term. Interestingly, the authors found a direct relationship between higher carbohydrate intakes and increased mortality and cardiovascular events (bad things). They also reported no adverse consequences of replacing carbohydrates with fat and protein foods from animal sources and/or saturated fat.
So it doesn’t look very promising for carbohydrates. However, this is the kind of pseudoscience we need to be careful with. For starters, even if a high carbohydrate diet is bad for you, it doesn’t automatically infer that a very low carbohydrate is good for you. These need to be studied individually.
However, not is all as it seems with this study when we delve a little deeper. A common problem with studies looking at carbohydrates, is they do not define the type of carbohydrates the participants were eating. With a 135,000 people, there’s probably a broad spectrum of dietary practices. However, many of the countries and people studied were from lower socioeconomical areas or countries. This means the majority of their dietary intake was from inexpensive refined carbohydrates. Something we already know is not good for our health.
Therefore, defining the type of carbohydrates the participants were eating in each of the studies included in this review would help inform us of the overall effect.
Our second study was published after the PURE study. This study included less participants but at 15,000 people over 25 years, it was pretty good. The nice thing about this study was it looked at carbohydrate intakes across the whole spectrum.
Here’s what this study found.
If your not a graph person let me explain this to you. Harzard ratio on the left looks at risk of health hazards. If the hazard ratio is above 1 it means greater risk and if it is below 1 it means lower risk. A hazard ratio of exactly 1 means no greater risk.
As you can see the greater risk for all cause mortality (death by all causes) is actually greatest in carbohydrate intakes of under 20%. This is more representative of the keto diet.
As the percentage of total carbohydrate intake increases there is a steady drop in risk until around 50% of total energy intake. Here the participants were at no greater risk of dying. As carbohydrates start to make up more of the total energy intake above 55-60% the risk begins to increase again (but it may also reduce risk as you can see from the graph).
This difference is likely once again related to the quality of carbohydrate chosen. If you choose a more fibrous and healthy carbohydrate your risk continues to drop. This is consistent with all other articles I’ve ever read on this topic. If you choose highly processed refined carbohydrates, your risk increases.
The researchers also found one crucial point. The higher risk associated with low carbohydrate diets was only seen if carbohydrates were replaced with animal sources of fat and protein (meat, cheese, butter etc). When replacing with plant protein and fat (beans, pulses, lentils, nuts, oils etc) the risk was removed.
What this means
Historically, the focus has been on an increased fat intake when discussing negative health effects of diets like the keto diet.
The jury is out on whether this is true. I have previously looked into this in some death if you’re interested and you can find this here.
I think we need to look a little further than just fat. Diet is interconnected and focusing on only one nutrient is rarely helpful.
People that follow low carbohydrates diets like a keto diet simply cannot be eating much fibre. The diet is mainly animal protein based. To remain in ketosis, there is little margin for any starch, fruits and there are very limited options with vegetables.
If we want to be scientific about things and use evidence to consider the pros and cons of a keto diet, then we also need to consider all the medical literature about diet.
What is clear when we do this is eating around 30g of fibre per day from good quality sources of carbohydrate, disease risk is lowered. Diabetes, cardiovascular disease, cancer, obesity, sleep apnoea and the list goes on, are all lowered by eating lots of fibre.
The temptation, when talking about carbohydrates, is to only consider highly processed options like white grains and sugar. However, carbohydrates exist in wholegrains, vegetables, fruits and legumes and these have been shown to be beneficial for our health.
I hope you found this article useful. I’ve tried to remain impartial and explain the pros and cons as the evidence presents them.
I think some people can do very well on a keto diet. My personal opinion is if someone is morbidity overweight and a keto diet helps them lose weight, this is ultimately better for their health.
Just keep in mind, in diabetes there are some big reasons to avoid going into actually ketosis if you’re taking SGLT-2 inhibitors and/or have type 1 diabetes. This can be dangerous and so eating just above ketosis may be a better idea. You can still achieve most of the benefits explained above, especially with regards to weight loss and not spiking your glucose levels. None of those benefits are ketosis specific.
However, if we assess the overall effects of such diets on a longer term basis and expand our gaze, the outcomes may be less favourable.
This likely represents what is missing from the diet rather than what is included in the diet. It’s quite clear in the evidence. Good quality carbohydrates provide a beneficial effect on our health. Cutting out almost 2 foods groups entirely (3 if we count high sugar – though this isn’t good for us anyway) may help you lose weight but it doesn’t automatically reduce your risk from all cause mortality. This is something replicate in the studies I have read on the matter.
Nonetheless, if you have all the information it means you can make an informed decision about your diet and which strategy you want to follow.