Pros and cons of the keto diet

By Deborah Lee on July 1st, 2024

You’ve no doubt heard of the keto diet? It’s a buzzword these days, especially after the tragic death of Dr Michael Mosley whose famous diet, the Fast 800 diet, is a keto diet. 

These kinds of terms can be confusing, so in this post, I’m going to make everything crystal clear. If you want to lose weight, you can have a think about it and decide if this is the diet for you.

What is a keto diet?

Keto stands for ketogenic. A ketogenic diet forces the body to burn fat instead of carbs to produce energy. As a result, byproducts are formed which are called ketones. The main ketones are beta-hydroxybutyrate and acetoacetate (which smells like pear drops). You might smell this on the breath of anyone doing a keto diet.

Normally, the human body gets most of its energy from the carbs in your diet. But if you stop eating carbs, your body uses up what it has quite quickly.  When there are no carbs left, the body has no choice but to burn fat for energy instead. 

This is the basis of the keto diet – cutting back on carbs to ensure fat is now the main energy source. This metabolic state is called being in ketosis.

When you first start a keto diet, it takes 3-7 days to get into ketosis. You can check for ketosis by using urine dipsticks called ketostix.

What are the pros of the keto diet?

Loose weight without counting calories

A keto diet is relatively easy to follow as there is no calorie counting. You eat real food and choose low-carb recipes. The diet will be moderate-protein, high-fat and contain very few carbs. This means sticking to a list of specific foods and being careful with portion control.

You need to keep your carb intake at less than 50g (some say 30g) per day. If you don’t do this, you will fall out of ketosis and stop losing weight

Humans are happy in ketosis

You might think ketosis isn’t good, but you would be wrong. The human body is happy in ketosis. Blood glucose levels are low, and insulin secretion is reduced, so the diet is particularly suitable for anyone with prediabetes, type-2 diabetes and metabolic syndrome. This is referred to as nutritional ketosis, which I must point out, is totally different to the dangerous ketoacidosis seen in uncontrolled diabetes. 

Don’t feel hungry

Interestingly, ketones help you not to feel hungry.  It affects the hunger hormones, ghrelin and leptin. Ketosis impairs the usual rise of ghrelin after a meal, which means the brain is not getting signals you need to keep eating. Also, the brain becomes more sensitive to leptin so it perceives you need to eat less.

Lose ten pounds in 2 weeks

Weight loss is rapid  to start with. In the first 2 weeks on a keto diet, you may well lose 10 pounds, which is far more than a standard low-calorie diet. In fact, as time passes, weight loss plateaus and at the end of the diet most people have lost a similar amount to people following different diets. However, the initial weight loss can be very good for morale and spur you on to keep going.

Lean mass is maintained

Inevitably when we go on any weight-losing diet, we lose muscle (lean body mass). But the good news is that evidence shows a keto diet is more likely to spare muscle loss than some other diets. It may be that ketosis stimulates the uptake of amino acids (the building blocks of protein) from the bloodstream.

Good for losing visceral fat

Visceral fat is a dangerous fat, deep in the abdominal cavity, that cushions the internal organs. This is sick fat which produces hormones that induce chronic inflammation and cause insulin resistance. Many studies have shown the keto diet is good at reducing visceral fat. 

In one 2019 study, 20 obese, female participants, followed a keto diet for 8 weeks. At the of the study, their BMI has reduced from an average of 32.19 to 27.76. They had lost a significant amount of visceral fat, without any change in their lean body mass. Levels of the neuropeptide, orexin-A, were significantly raised. This is known to be linked to appetite control, metabolic rate, and sleep, and also helps regulate the inflammatory response. In obesity, levels of orexin-A are often low.

Lowers blood pressure

The keto diet lowers your blood pressure. A 2013 meta-analysis concluded that following a low-carb diet of less than 50g carbohydrates per day was significantly better at lowering diastolic blood pressure (the lower reading) than a low-fat diet.

Lowers cholesterol

The keto diet generally lowers cholesterol. High cholesterol levels are associated with atherosclerosis – this is the process in which fatty plaques are laid down in artery walls and gradually block the arterial blood supply. Atherosclerosis is the basis of cardiovascular disease – heart disease and stroke. 

The keto diet has a favourable effect on cholesterol in that it raises HDL (‘good’) cholesterol and lowers triglycerides. 

However, on the downside, it is known to raise LDL (‘bad’) cholesterol. The significance of this is not known, but this is one reason the diet should not be continued long-term without medical supervision.

Lower blood sugar

The keto diet is particularly suited to those with diabetes as it lowers levels of fasting insulin and reduces insulin resistance. Doing this reduces the amount of diabetic medication needed. Studies in type-2 diabetes have shown the keto diet lowers HbA1c (glycosylated haemoglobin) levels – these are a common marker of blood glucose control.

The keto diet has been studied in patients with type-1 diabetes, with good results. However,  hypoglycaemia is not uncommon and close glucose monitoring is mandatory. Anyone with type-1 diabetes who wants to start a keto diet must take advice from their diabetic specialist before starting.

Improves other medical conditions

PCOS – Women with PCOS often have insulin resistance and raised androgen levels. The keto diet can be very helpful. In a 2002 study, a group of women with PCOS and a BMI of 27 or over, followed a keto diet for 24 weeks. After the study, they had lost an average of 12.1% of their body weight, along with having significant reductions in insulin and free testosterone levels.

Epilepsy – Studies show a keto diet can reduce the frequency of seizures in children, but this has not been established in adults.

Cognition – Research suggests a keto diet can reduce cognitive decline.

AcneAcne tends to improve as there is a reduction in skin inflammation.

CancerCancer cells cannot use ketones for fuel. Hence a low-carb diet is sometimes recommended for cancer sufferers although there are few studies to date to substantiate this.

the cons of the keto diet

Keto flu

It’s not uncommon to have side effects when first getting into ketosis known as keto flu. These symptoms include headache, fatigue, nausea, dizziness and brain fog. It usually only lasts a week or so. Drink more water, eat enough calories and rest as much as possible. It will pass.

Kidney disease

A diet high in animal fat increases the excretion of calcium in the urine and increases the risk of kidney stones. A keto diet is not suitable for anyone with chronic kidney disease.


 It may be difficult to eat 30 g of fibre per day on a keto diet. Make sure you eat foods that are high in fibre but low in carbs. These include veg such as broccoli, cauliflower and courgettes, nuts and seeds, chia seeds, flax seeds and berries. You might want to take a fibre supplement such as psyllium.

Nutritional deficiency

Some research suggests that following a keto diet can lead to some vitamin and mineral deficiencies, so it is advisable to take a vitamin and mineral supplement when on a keto diet.

Hypoglycaemia (low blood glucose)

Anyone with type-1 or type-2 diabetes should seek medical advice before starting a keto diet. They must test their blood glucose levels more often.

Bone loss

Studies of the keto diet in animals have shown it causes bone loss, but this has not been reliably demonstrated in humans. However, if you are at risk of osteopenia or osteoporosis, such as peri or postmenopausal women, always consult your GP. You may be advised to take calcium and vitamin D supplements.

Not safe for women pregnant or trying to conceive

A keto diet is not recommended for women pregnant or trying to conceive. A low-carb diet means not eating things like bread and cereal that are fortified with folic acid, which is vital for the growing fetus. The metabolic state of ketoacidosis in the mother can affect the growth of the embryo or fetus.

Not ideal if breastfeeding

Although a keto diet is possible when breastfeeding,  it may be impossible to take in enough calories and nutrients, and it can reduce the supply of breast milk.


I think the keto diet is a great option for anyone who wants to lose weight and has given up in the past due to slow weight loss and tedious meal plans. Keto recipes are often delicious, and there are some excellent, fun, meal ideas. Once ketosis is established, you feel well, and the weight seems to fall off.  

It seems to me that the pros of the keto diet outweigh the cons. If you have any health condition, always consult your GP first.

However, it is vital to count the carbs and keep the carb intake very low or weight loss will stop.

For more information, visit Dr Fox Online Pharmacy.

Deborah Lee

Having worked for many years in the NHS, initially as a GP, and then as Lead Clinician for an integrated Community Sexual Health Service, Dr Deborah Lee now works as a health and medical writer, with an emphasis on women's health and is s a menopause specialist.

All articles by Deborah Lee

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