cons of keto diet

Cons of the ketogenic diet

This article summarises some of the potential drawbacks associated with the ketogenic diet.

The individualised response to food is very variable and you need to choose foods and dietary habits that are perfectly right for you. By being aware of the drawbacks, you are better informed and in the position to make your diet successful for you.

Dehydration / electrolyte imbalance

When you go on the ketogenic diet you dramatically reduce carbohydrate intake, as well as depleting glycogen levels (stored carbohydrate). Since the body stores water with carbohydrate, this results in increased water excretion and electrolytes (important substances that help to regulate the balance of fluids in the body) in particular sodium, potassium and magnesium. Also being in nutritional ketosis means that insulin levels are reduced and so as a result, the kidneys increase sodium excretion. So ultimately, the net result of being on the ketogenic diet, especially at the beginning can be dehydration and electrolyte imbalance. This can often result in symptoms such as muscle cramps, fatigues, headaches and may be a key reason for experiencing the ‘keto flu’ (other factors include the transitory period while your body adjusts to being able to burn fat).

Tip: ensure you are adequately hydrated, especially during the keto transition – so drink before you become thirsty. Make sure you replenish electrolyte levels: sodium – salt your food; include potassium rich foods – avocado, bone broth, courgettes, mushrooms; include magnesium rich foods – pumpkin seeds, dark chocolate/cacao; include calcium rich foods – leafy greens, broccoli, salmon. Consider electrolyte supplements, especially if you are exercising. Of course, if you are on any medications for blood pressure/heart/kidney problems, ensure you seek medical advice first.

Blood lipid and cholesterol levels

Studies show blood levels of fat and fat transporters (blood lipid and cholesterol) to be varied in response to the ketogenic diet. Since these may be some of the risk factors associated with cardiovascular disease (CVD), it’s important to know where you stand. Some studies show no change (1), some studies show reduced triglyceride levels (2), some studies show increased high density lipoprotein cholesterol (HDL-C) and low density lipoprotein cholesterol (LDL-C) (3). There are many reasons why these responses may be so variable and one is diet composition. The quantity and composition of fats as well as sources of protein and fibre intake will all affect cholesterol levels. Different studies have different dietary composition, impacting the outcomes. Also some people have a genetic defect which means that they have excessively high cholesterol levels (hypocholesteraemia) and some people are hyper responders to saturated fats and are therefore likely to have a significantly elevated LDL-C response to the ketogenic diet (4).

Another factor which might temporarily increase blood cholesterol levels is the weight loss that is usually associated with the ketogenic diet. Since the role of HDL-C and LDL-C is to transport fat around the body, if you drastically increase dietary fat, as well as breaking down your own body fat, your body will obviously have a lot more fat to transport around! However, this may just be a temporary increase which isn’t necessarily anything to be concerned about.

I would note that saturated fat is not ‘bad’ and it’s important to consider its role within a wider context – what does your weekly diet consist of? What type of fats do you eat? Also be aware of other key risk factors associated with CVD such as inflammation and how you manage those.

Tip: if you have any concern of hypocholesteraemia/ genetic predisposition to high cholesterol/increased CVD risk seek medical advice. Otherwise be mindful of the types of fat you eat and focus on sources of monounsaturated fats such as avocado, olives and macadamias. Be aware of the quantity of the fat you ingest (you want enough but no need to go crazy) and ensure you eat enough protein and non-starchy vegetables.

Low thyroid hormones

Studies show an association between the ketogenic diet and reduced active thyroid hormone (T3) levels (5,6). However, few studies conclude that this association is representative of thyroid dysfunction/hypothyroidism (7). Many studies show that although the ketogenic diet is associated with reduced T3 levels, other symptoms that may reflect hypothyroidism, such as elevated TSH levels (thyroid stimulating hormone), reduced metabolic rate or the inability to lose weight (8) are not displayed.

Although unclear why this could be the case, one function of thyroid hormones is in the metabolism of carbohydrate. Therefore a reduction in T3 levels may be reflective of reduced carbohydrate intake and an increased tissue sensitivity to T3, rather than reflecting any clinical significance. Additionally, reduced T3 levels occur during excess calorie reduction and/or weight loss, which are usually associated with being on the ketogenic diet. Also chronic stress may indirectly reduce thyroid function (9).

Tip: be realistic about the amount of stress you’re under – whether it is personal, financial, training etc. – it all ultimately affects you the same. Take action now to reduce those stresses! If your objective is to lose weight then reduce calories gradually and sustainably and perhaps avoid reducing calories for the first week or two. If you have any concerns, as in you are experiencing hypothyroidism symptoms, seek medical advice. Otherwise, if you feel good, enjoy the journey!

Risk of low energy availability

It’s a bit of a double-edge sword. The ketogenic diet is hailed as a great way to lose weight and studies show that people end up cutting calories unintentionally (10) and have suppressed appetite (11). Whilst this may be beneficial for someone who is in an energy surplus and/or has excess body fat to lose, this may be detrimental for someone who is not in this position (e.g. lean, exercising, currently maxing out on their available energy). Energy availability is the energy your body needs to carry out physiological functions and work optimally – so the energy left after your body has utilised all its energy to stay alive and carry out exercise. Low energy availability (LEA) affects a variety of critically important processes in health such as immune and menstrual function, bone growth, cardiovascular function etc. Therefore if you have LEA, you will suffer adverse health consequences e.g. low energy, loss of bone density (osteopenia, osteoporosis), reduced sexual libido (loss of periods, fertility) and likely to become ill repeatedly etc.

Tip: consider who you are! If you are already lean, exercise a fair amount, or may be only just hitting your energy needs, approach the ketogenic diet with caution. Make sure you are aware of eating enough and monitor yourself.

Final words

  1. Check out: Pros of the ketogenic diet to explore the health benefits associated with going keto.
  2. Mitigate the cons: focus on a well formulated quality ketogenic diet comprising whole foods: include lots of non-starchy vegetables, quality sources of good fats (avocados, olives), and make sure you attend to your electrolyte and hydration needs.
  3. Personalisation is key: think of the ketogenic diet as a template and then adapt it where you can to suit you and your needs, goals and preferences best.

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This article was written by Antonia Osbourne.
You can read more of Antonia’s articles and learn about her specialist areas and experiences using the link below.
More about Antonia


  1. Naude et al. (2014). ‘Low carbohydrate versus isoenergetic balanced diets for reducing weight and cardiovascular risk: a systematic review and meta-analysis.’
  2. Bueno et al. (2013). ‘Very-low-carbohydrate ketogenic diet v. low-fat diet for long-term weight loss: a meta-analysis of randomised controlled trials.’
  3. Sackner-Bernstein et al. (2015). ‘Dietary intervention for overweight and obese adults: comparison of low-carbohydrate and low-fat diets.’
  4. Masson et al. (2003). ‘Genetic variation and the lipid response to dietary intervention: a systematic review’
  5. Phinney et al. (1983). ‘The human metabolic response to chronic ketosis without caloric restriction: preservation of submaximal exercise capability with reduced carbohydrate oxidation.’
  6. Volek et al. (2002). ‘Body composition and hormonal responses to a carbohydrate-restricted diet.’
  7. Lee et al. (2017). ‘Longitudinal change in thyroid hormone levels in children with epilepsy on a ketogenic diet: prevalence and risk factors.’
  8. Bisschop et al. (2001). ‘Isocaloric carbohydrate deprivation induces protein catabolism despite a low T3-syndrome in healthy men.’
  9. Smith et al. (2006). ‘The role of the hypothalamic-pituitary-adrenal axis in neuroendocrine response to stress.’
  10. Vargas-Molina et al. (2020). ‘Effects of a ketogenic diet on body composition and strength in trained women.’
  11. Sumithran et al. (2013). ‘Ketosis and appetite-mediating nutrients and hormones after weight loss.’

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