Types of diets: young woman stood in her kitchen eating

Types of diets: benefits & pitfalls of GF, Keto, Vegan & Low FODMAP

With the progression of nutrition research and the desire for many people to find the key to their health, there has been a rise in the number of people who try different types of diets. Many of these have been labelled as fad diets, however some can be beneficial for both health and the environment. This blog investigates the benefits and pitfalls of different ways of eating and when they may be appropriate for you or your clients.

No one size fits all when it comes to choosing different types of diets

It is important to note that when it comes to an optimal diet, although there are some factors that are always beneficial, there is no one size fits all. It is documented by researchers who look at traditional types of diets that some genetic profiles, such as those that evolved in tropical climates, are more suited to plant-based diets and others, such as Inuit populations, have evolved to utilise a high fat, low fibre diet.

Although we are more likely to be working with individuals with a diverse gene pool, dietary interventions should be considered on an individual basis. Having said this, consuming wholefoods and including a high diversity and amount of plant-based food is consistently found to be beneficial to health.


Skip to Key Takeaways

Vegan diets

Definition: excludes all foods derived from animals and vegans typically do not use other animal products

Vegan diets are becoming increasingly popular as they are considered to be less harmful to the environment and have a lower impact on climate change. It is also widely thought that they are healthier.

However, it is inaccurate to simply state that vegan diets are healthy. Many make the decision to follow a very natural diet of healthy vegetables, fruits, nuts, seeds and wholegrains, and frequently eat foods wonderfully rich in a whole host of natural nutrients such as the phytonutrients, fibre, folate, magnesium, potassium and vitamins C and E.1 However, there is also an increase in the amount of available “vegan junk food,” which is heavily processed and very high in refined carbohydrates and trans fats.

Benefits of this type of diet

A high intake of fruit and vegetables has been linked in numerous studies with health benefits including a reduction in risk of a number of diseases such as cardiovascular disease2 and diabetes.3 Various mechanisms for this risk reduction have been proposed including that the high levels of antioxidant vitamins reduce oxidative stress. The phytonutrients in plant-based diets have a strong synergistic antioxidant action. In addition, fibre has many benefits for health.

A report published in The Lancet in 2019 concluded that a dietary shift toward plant foods and away from animal products is vital for promoting the health of our planet.4 The report states that projections for the future show that “vegan and vegetarian diets were associated with the greatest reductions in greenhouse-gas emissions.” Therefore, opting for a vegan diet is often an ethical and environmental decision as well as a potentially healthful one.


Vegan diets need to be carefully planned to ensure adequate intake of protein, B12, vitamins A & D, iodine, iron, zinc, calcium and omega-3 fatty acids. However, it’s not just people following a vegan diet who can be low in these nutrients, the National Nutrition and Diet Survey (2013/14)5 showed significant numbers of the population are low in omega-3 fatty acids, vitamin D, vitamin B12, riboflavin and iron (teenage girls and pre-menopausal women in particular are low in iron).

Type of diet – Ketogenic

Definition: diet low in carbohydrate and high in fat

High fat, ketogenic diets are being used therapeutically for a number of health conditions including Alzheimer’s, epilepsy, cancer and obesity. Ketosis is where the body burns ketones – derived from fats.6

A ketogenic diet is high in fat, moderate in protein and very low in carbohydrate which causes the body to behave in a similar way to periods of limited food availability. The diet is composed of around 65% – 80% fat with carbohydrate and protein constituting the remainder of the intake.

Between meals, as well as during fasting, starvation and strenuous exercise, when blood glucose levels fall, fatty acids are released from adipose tissue and can be used by most cells as a fuel source (except brain cells which are unable to uptake fatty acids). In the liver some fatty acids are formed into ‘ketone bodies’ – acetoacetate which is then further metabolised to beta-hydroxybutyrate and acetone. Ketone bodies can be used by tissues, including the brain, as a source of fuel.

Benefits of a ketogenic diet

The ketogenic diet, if done correctly, can be an ‘anti-inflammatory’ way of eating. When we eat carbohydrate our blood sugar increases, and this creates some level of inflammation in the body. Ketogenic diets can:6–12

  • Lower blood sugar (and thus lower inflammation) and reduce the risk of metabolic syndrome and diseases associated with it
  • Control appetite – ketosis affects ‘hunger’ hormones and allows us to feel full for longer. In contrast, eating a lot of carbohydrates can have the opposite effect
  • Help with weight loss
  • Support memory – research is showing the benefit of ketogenic diets in symptomatic relief from Alzheimer’s and ketosis may have disease-modifying activity through a number of different mechanisms.
  • Improve physical stamina – ketogenic diets are used by some sportsmen for endurance events
  • Improve sleep, immunity, anxiety, mood and overall feeling of wellbeing
  • Support those with epilepsy – The ketogenic diet has long been associated with helping to manage epilepsy


Some diets which are ketogenic are not recommended, i.e., diets which are high fat but place little emphasis on the types of fats included (i.e., they allow processed and inflammatory fats) and diets which encourage protein and fat intake at the expense of vegetables.

The majority of people can safely go on a well-planned ketogenic diet, however, those with serious medical conditions should only undertake these types of diets under the supervision of a health professional. The diet may not be suitable for those with diabetes, thyroid and liver disease. For example, people with diabetes are at risk of developing a condition called diabetic ketoacidosis, which can be fatal.

For anyone embarking on a ketogenic diet it is recommended that blood monitoring is undertaken at the start and after 2 to 3 months to monitor and check for any adverse changes. Tests to include: Complete blood count, fasting blood sugar, HbA1c, fasting lipid panel, thyroid panel, liver function, kidney function and electrolytes.

Other disadvantages can be:

  • Feeling unwell in the first few days of changing to this diet – referred to as Keto Flu. This can be helped by eating some salt daily and staying hydrated (urination may increase for a few days).
  • Increasing fat in the diet and the addition of MCT oil can lead to intestinal symptoms
  • Long periods of ketosis can result in loss of muscle and increased fat
  • Whilst the brain can run on ketones it does require a small amount of glucose. So, after a few weeks of being in ketosis, it may be preferable to eat a larger amount of carbohydrates on 1 or 2 days per week (e.g., a sweet potato and couple of portions of fruit).
  • The intake of certain micronutrients may be lower on a ketogenic diet13

Gluten free diets

Definition: removal of all gluten

Gluten is found in – wheat, barley, rye – bread, pasta, cous cous, some soy sauce, Worcester sauce, some rice sushi, pub chips, flour products.

Wheat is a staple carbohydrate in Western diets, often being consumed in some form at every meal and snack. It contains a protein called gluten. Gluten is also found in rye and barley. Oats contain no gluten as such, but since oats are often grown and processed along with wheat, most conventional oat products contain traces of gluten.

Many people do report feeling better when they switch to a gluten-free diet and there is no question that eating gluten-free is definitely a healthier option for some people. However, swapping an ‘unhealthy’ wheat-filled diet for an ‘unhealthy’ gluten-free diet will not lead to improvements in health and one study found may lead to lower fibre intake14.

When eliminating gluten containing foods, it is important to replace them with nutrient dense, wholefoods that are naturally gluten-free.

Benefits of gluten free diets

The protein gluten cannot be digested by humans and increases gut permeability (i.e., leaky gut) for a while after it is eaten. This happens to some degree in everyone every time foods containing gluten are eaten. This can lead to an immune response and be a contributory factor in inflammation.

A healthy body will ‘mop up’ the inflammation and repair the leakiness of the gut until gluten is eaten again and the process starts again. However, because gluten containing foods are often eaten at every meal and snacks in between – the body’s capacity to ‘repair’ the gut after eating these foods may be exceeded, and this can increase the likelihood of developing a sensitivity to gluten – a condition referred to as ‘non-coeliac gluten sensitivity’ (NCGS) which is linked to many conditions and symptoms can include anxiety, depression, skin eruptions, bloating, constipation and/or diarrhoea and more15,16.

Gluten can also trigger an autoimmune condition in the small intestine called coeliac disease (CD)17whereby the cells (enterocytes) lining the digestive tract are severely damaged and inflamed and digestion is significantly impaired. The only treatment for this is to completely avoid gluten. Other conditions associated with CD include dermatitis herpetiformis, a violent, blistering rash, or gluten ataxia, which may lead to neurological problems and loss of coordination.18

Drawbacks of this type of diet

Wheat does offer some benefits for health – it is high in fibre and also provides some B vitamins and minerals. In the average diet wheat-based products provide 78% of the dietary fibre, therefore very often, when a person removes gluten from their diet, they also remove the fibre.

Many GF products on the market are heavily processed, have a very high glycaemic load and are low in fibre. However, it is more than possible to get a good intake of fibre from non-gluten sources such as vegetables, fruit, brown rice, quinoa, buckwheat, nuts and seeds.

Types of diet – Low FODMAP

Definition: avoidance of certain fibres known as FODMAPs (see below)

FODMAPs are dietary sugars and carbohydrates which are easily fermented by the bacteria and can exacerbate symptoms of gas, bloating and pain. Therefore, low FODMAP diets are utilised for those with certain digestive issues.19,20

FODMAPs stand for:

  • Fermentable
  • Oligosaccharides (e.g., Fructans found in wheat, garlic, onion and chicory etc. and galactans found in legumes, including beans, peas and lentils)
  • Disaccharides (e.g., Lactose found in milk products)
  • Monosaccharides (e.g., excess Fructose found in fruits, honey, high fructose corn syrup etc.)
  • And
  • Polyols (found in sweeteners containing isomalt, mannitol, sorbitol, xylitol plus stone fruits such as avocado, apricots, cherries, nectarines, peaches and plums)

After excluding high FODMAP foods for a month, foods from each FODMAP group should be reintroduced, one at a time (e.g., foods containing fructose, then foods containing lactose etc.). During the reintroduction symptoms should be monitored and if a FODMAP group of foods causes problems then continue to eliminate this group.

Benefits of this type of diet

Low FODMAP diets can be very effective at improving symptoms in many individuals with digestive disorders, particularly IBS and small intestine bacterial overgrowth (SIBO).21,22 In some people ingested FODMAP carbohydrates are not absorbed as they should be in the small intestine, instead they pass through the far end of the small intestine and into the large intestine.

FODMAPs act as fast food for the bacteria which give off a lot of gas as they ferment the food. The gas makes large intestine swell and experience bloating. Another problem is that FODMAPs can draw fluid into the intestine. Pain and watery urgent diarrhoea can result. In other cases, changes to fluid and gas production are associated with constipation.

Some FODMAPs may be tolerated in the diet, it is the total load from all sources that causes a problem. This may be from a large quantity of a single food or smaller amounts of several different FODMAP foods added together over a period of time (e.g., over a day or a few days).

Disadvantages of a FODMAP diet

A low FODMAP diet involves initially restricting a considerable number of foods which some may find very difficult; however, it is not intended to be a long-term diet and because of the restrictive nature and complexity it is best done with the guidance of a practitioner. The restriction of FODMAPs for a long period of time can lead to a reduced dietary diversity of plant-based fibre which has an impact on the diversity of the gut microbiome (a diverse microbiome is linked to good health).23

Types of diets – a note on alternatives

All the above dietary interventions involve the removal or reduction of certain foods or food groups. The food industry is well aware of this and therefore has developed many replacements for these.

As already alluded to, these alternatives are less healthy than the food that is removed as the alternatives provided can be heavily processed, high in sugar or refined carbohydrates and inflammatory oils. Therefore, if choosing to remove anything from the diet it is still important to opt for fresh, wholefoods which are naturally free of whatever is removed.

Elimination diets?

Some may be removing food from the diet as they feel it is causing them an issue such as allergy or intolerance. If this is the case, it is recommended to follow an elimination diet. Where common allergens are removed and reintroduced one at a time whilst monitoring symptoms.

If you feel that an elimination diet may be required you can find more information at our blog: Elimination Diets – Pinpointing the Source of Undiagnosed Symptoms

Key takeaways

  • Vegan diets are popular as they can have a positive impact on health due to high intake of plant-based foods, there is also evidence that is has a lower impact on the environment and climate change. However, vegans are at a greater risk of nutrient deficiencies (including protein, essential fatty acids, B12, iodine, zinc and iron) and therefore should be well planned.
  • Ketogenic diets are high fat, low carbohydrate aimed at stimulating ketosis, using fat for fuel. Research suggests it is beneficial for many conditions including weight loss, diabetes, cardiovascular disease as well as neurodegeneration (dementia) and epilepsy. However, poor ketogenic diets (high processed fat and or low in fibre) can be detrimental to health. There can also be many side effects and therefore it needs to be well managed.
  • Gluten has been shown to influence many digestive issues and can trigger the autoimmune condition Coeliac disease in some individuals. Recent research also suggested that gluten sensitivity may also affect neurological function. Hence, gluten free diets can be effective for many. When removing gluten (found in wheat, rye, barley, oats and spelt) it is important to ensure adequate fibre is still obtained, preferably form fruits and vegetables.
  • FODMAP stands for fermentable oligo-, di- and mono-saccharides and polyols, found in many fibrous foods. These are easily fermented by the bacteria and can exacerbate symptoms of gas, bloating and pain. Therefore, low FODMAP diets are utilised for those with certain digestive issues, particularly IBS and SIBO. However, the removal of these foods should only be temporary as they play an important role in supporting the diversity of the microbiome. Therefore, they should be reintroduced gradually following removal.
  • Alternatives to food removed are often less healthy than the food that is removed as can be heavily processed, high in sugar or refined carbohydrates and inflammatory oils. Therefore, if choosing to remove anything form the diet it is still important to opt for fresh, wholefoods which are naturally free of whatever is removed.

Types of diets references

  1. Craig WJ. Health effects of vegan diets. Am J Clin Nutr. 2009;89(5). doi:10.3945/AJCN.2009.26736N
  2. Aune D, Giovannucci E, Boffetta P, et al. Fruit and vegetable intake and the risk of cardiovascular disease, total cancer and all-cause mortality-a systematic review and dose-response meta-analysis of prospective studies. Int J Epidemiol. 2017;46(3):1029-1056. doi:10.1093/IJE/DYW319
  3. Satija A, Bhupathiraju SN, Rimm EB, et al. Plant-Based Dietary Patterns and Incidence of Type 2 Diabetes in US Men and Women: Results from Three Prospective Cohort Studies. PLoS Med. 2016;13(6). doi:10.1371/JOURNAL.PMED.1002039
  4. Willett W, Rockström J, Loken B, et al. Food in the Anthropocene: the EAT–Lancet Commission on healthy diets from sustainable food systems. The Lancet. 2019;393(10170):447-492. doi:10.1016/S0140-6736(18)31788-4
  5. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/551352/NDNS_Y5_6_UK_Main_Text.pdf.
  6. Dowis K, Banga S. The Potential Health Benefits of the Ketogenic Diet: A Narrative Review. Nutrients. 2021;13(5). doi:10.3390/NU13051654
  7. Batch JT, Lamsal SP, Adkins M, Sultan S, Ramirez MN. Advantages and Disadvantages of the Ketogenic Diet: A Review Article. Cureus. 2020;12(8). doi:10.7759/CUREUS.9639
  8. Davis JJ, Fournakis N, Ellison J. Ketogenic Diet for the Treatment and Prevention of Dementia: A Review. J Geriatr Psychiatry Neurol. 2021;34(1):3-10. doi:10.1177/0891988720901785
  9. Lilamand M, Mouton-Liger F, Paquet C. Ketogenic diet therapy in Alzheimer’s disease: an updated review. Curr Opin Clin Nutr Metab Care. 2021;24(4):372-378. doi:10.1097/MCO.0000000000000759
  10. Pietrzak D, Kasperek K, Rękawek P, Piątkowska-Chmiel I. The Therapeutic Role of Ketogenic Diet in Neurological Disorders. Nutrients. 2022;14(9). doi:10.3390/NU14091952
  11. Li RJ, Liu Y, Liu HQ, Li J. Ketogenic diets and protective mechanisms in epilepsy, metabolic disorders, cancer, neuronal loss, and muscle and nerve degeneration. J Food Biochem. 2020;44(3). doi:10.1111/JFBC.13140
  12. Zhou C, Wang M, Liang J, He G, Chen N. Ketogenic Diet Benefits to Weight Loss, Glycemic Control, and Lipid Profiles in Overweight Patients with Type 2 Diabetes Mellitus: A Meta-Analysis of Randomized Controlled Trails. Int J Environ Res Public Health. 2022;19(16). doi:10.3390/IJERPH191610429
  13. Dr Mercola. Fat for Fuel .; 2017.
  14. Fry L, Madden AM, Fallaize R. An investigation into the nutritional composition and cost of gluten-free versus regular food products in the UK. J Hum Nutr Diet. 2018;31(1):108-120. doi:10.1111/JHN.12502
  15. Ford RPK. The gluten syndrome: a neurological disease. Med Hypotheses. 2009;73(3):438-440. doi:10.1016/J.MEHY.2009.03.037
  16. Sapone A, Bai JC, Ciacci C, et al. Spectrum of gluten-related disorders: Consensus on new nomenclature and classification. BMC Med. 2012;10(1):1-12. doi:10.1186/1741-7015-10-13/FIGURES/4
  17. Pes GM, Bibbò S, Dore MP. Coeliac disease: beyond genetic susceptibility and gluten. A narrative review. Ann Med. 2019;51(1):1. doi:10.1080/07853890.2019.1569254
  18. https://www.mayoclinic.org/diseases-conditions/celiac-disease/symptoms-causes/syc-20352220.
  19. Pessarelli T, Sorge A, Elli L, Costantino A. The low-FODMAP diet and the gluten-free diet in the management of functional abdominal bloating and distension. Front Nutr. 2022;9:1007716. doi:10.3389/fnut.2022.1007716
  20. Dieterich W, Zopf Y. Gluten and FODMAPS-sense of a restriction/when is restriction necessary? Nutrients. 2019;11(8). doi:10.3390/nu11081957
  21. Wielgosz-Grochowska JP, Domanski N, Drywień ME. Efficacy of an Irritable Bowel Syndrome Diet in the Treatment of Small Intestinal Bacterial Overgrowth: A Narrative Review. Nutrients. 2022;14(16). doi:10.3390/NU14163382
  22. Więcek M, Panufnik P, Kaniewska M, Lewandowski K, Rydzewska G. Low-FODMAP Diet for the Management of Irritable Bowel Syndrome in Remission of IBD. Nutrients. 2022;14(21):4562. doi:10.3390/NU14214562
  23. Leeming ER, Johnson AJ, Spector TD, Roy CIL. Effect of Diet on the Gut Microbiota: Rethinking Intervention Duration. Nutrients. 2019;11(12). doi:10.3390/NU11122862

If you have questions regarding the topics that have been raised, or any other health matters, please do contact our team of Nutritional Therapists.

01684 310099


Last updated on 3rd January 2024 by cytoffice


7 thoughts on “Types of diets: benefits & pitfalls of GF, Keto, Vegan & Low FODMAP

  1. One thing you did not mention in your excellent coverage is the fact that many ‘health gurus’ do not practice what they preach particularly in the USA some pushing mega vitamin regimes that they profit from this being their motivation.
    Often less is more 🙂

  2. Interesting and easy to follow, thank you. I have just learned the name Non-coeliac gluten sensitivity, but have lived with this for 25 years. Doctors at that time seemed to have no idea what might be the cause of IBS and bloating. I eventually worked it out by elimination of food groups. I made my own bread till recently but now, Free From bread is easy to find – though mostly full of weird ingredients…. Have recently been told I’m pre-diabetic, though I have no sugar, and have cut my fruit intake. My weight is fine. Best keep things simple, eat mindfully, and stay calm!

    1. We are very glad you found the article helpful. If you would like further, individual dietary and supplement advice, in terms of both your gluten sensitivity and prediabetes, you are very welcome to get in touch with our team of nutritional therapists on nutrition@cytoplan.co.uk

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