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The Great Diet Debate

Updated: Nov 8, 2020

The Ketogenic, Palaeolithic, Mediterranean, and Vegan diets are popular diets today. It therefore requires an analysis of the pros and cons of these four diets, and with a critical and balanced perspective draw a distinct conclusion supported by evidence as to the healthiest diet. Nutrition is a very broad subject, so to draw this conclusion we will distinguish the position of each diet in accordance to what a healthy diet should be based on.

Healthy Criteria

• Low fat content - Randomised controlled trials that replaced saturated fat with polyunsaturated vegetable oil saw a decrease in cardiovascular disease by around 30%. This decrease was close to the same reduction experience using statin medication (Sacks et al., 2017).

• 50-55% carbohydrate - intake of 50-55% carbohydrate was associated with a minimal risk of mortality (Seidelmann et al., 2019).

• Nutritionally adequate – contains all nutrients within RDI of calories.

• Disease prevention – Diet helps fight /protect from lifestyle diseases.

• Unprocessed/Unrefined – Ensures nutrients and fibre are not removed from food.

• Environmental Impact - Food varieties show different environmental impacts on our environment with animal foods having a higher greenhouse gas emission than plant-based products. A diet that includes high calorie intake, refined/processed foods and/or animal products, and the chronic disease that is associated with this dietary pattern is unsustainable (Harvard School of Public Health, 2019d).

The Ketogenic Diet

The ketogenic diet was introduced in 1921 as an effective treatment for epilepsy in children who continue to suffer from seizures while on antiepileptic medication. It then became a popular weight loss diet for healthy people wanting to lose weight. The ketogenic diet is a low carbohydrate diet consuming less that 50g of carbohydrates each day. Some people choose to consume around 30g of carbohydrate just to ensure their body stays in ketosis. Ketosis is when the body commences burning fat for energy due to the lack of carbohydrates the body’s preferred energy food (, 2019a). On a ketogenic diet the daily kilojoules are broken into around 75% fat, 20% protein and 5% carbohydrates (Rudy Mawer, MSc, CISSN, 2018) to ensure a state of ketosis. On a calorie intake of 2000, this equals around 165 grams of fat, 40 grams of carbohydrate, and 75 grams of protein (Harvard School of Public Health, 2019a).

The pros of this diet are in its use as a medical treatment mostly used in children with poorly controlled epilepsy to aid in the reduction/severity of seizures. Improvement is often seen within weeks of commencing this diet (Epilepsy Action Australia, 2017). Another pro is in the consumption of food in its unprocessed state. Eating the food in its natural state allows for the required nutrients and fibre to be consumed.

The cons of the ketogenic diet are concerning as this diet has become an extremely popular diet for healthy individuals wanting to lose weight. Is it the miracle diet that we have all been looking for? It is reported that when weight is lost by reducing carbohydrates the body is mainly losing water and protein. Carbohydrates tend to bulk up the muscle with glycogen, while a low-carbohydrate diet drains the glycogen from the muscle removing the water resulting in rapid weight loss (Nutrition Facts, 2019).

The ketogenic diet claims that it may improve glucose levels for individuals with T2DM, however its high saturated fat content impairs insulin sensitivity and is linked to T2DM (Parry et al. 2017). A high fat diet may also be linked to obesity and chronic inflammatory diseases of the airway and lung (Rosenkranz, Townsend, Steffens, & Harms, 2010, p.499).

A short study over one day of adults who consumed a high-fat diet, overfeeding throughout the day, returned results of an impaired whole-body insulin sensitivity. These results show how quickly this overfeeding of high fat foods can have a negative effect on glucose metabolism (Parry, Woods, Hodson, & Hulston, 2017).

A meta-analysis suggests that meat and processed meat are associated with an increased risk of total mortality from cardiovascular disease and cancer (Pan et al., 2012).

Diets with either high or low amounts of carbohydrate have shown to be associated with an increased rate of all-cause mortality. A cohort study found the mortality was causally related to the source of protein and fat. If the source was from animal products it increased mortality, and if it was from plant products it decreased mortality. The study also found an intake of 50-55% carbohydrate was associated with a minimal risk of mortality (Seidelmann et al., 2019).

A diet that includes high calorie intake, refined/processed foods and/or animal products, and the chronic disease that is associated with this dietary pattern is unsustainable. Food varieties show different environmental impacts on our environment with animal foods having a higher greenhouse gas emission than plant-based products (Harvard School of Public Health, 2019).

In summary the ketogenic diet presents as a high fat, low carbohydrate diet that cannot supply the daily nutrients required. Though it does show health benefits for children with epilepsy, it is not supported as a diet for healthy individuals. The ketogenic diet can be associated with chronic disease with its claim of weight loss showing the loss of protein and water, with evidence showing a greater weight loss would be achieved on a low-fat diet. The diet is environmentally unsustainable with its high amounts of animal product consumed.

Palaeolithic Diet

The paleolithic diet consists of foods that were consumed in the paleolithic era. This diet supports the belief of returning to the hunter-gatherer diet that kept the cave men in good health approximately 2.5 million years ago (Mayo Clinic, 2017). Foods that are restricted on a Paleolithic diet include cereal grains, starchy vegetables, legumes, peanuts, dairy, refined sugar, processed foods, salty foods, and refined vegetable oils (, n.d.c). These foods did not exist in the paleolithic era and therefore are removed from the diet. There is some confusion as to what is included in the diet therefore there is not a true palaeolithic diet (Harvard School of Public Health, 2019c).

Low carbohydrate intake consists of low GI non-starchy fruit and vegetables that make up around 35-45% of the dietary calories of the palaeolithic diet. High fibre intake from these fruit and vegetables is also attained, with the exclusion of sodium salt intake (Patient, 2018).

The pros of the Palaeolithic diet is the reduction in salt that has been shown to reduce cardiovascular events and health costs, no dairy, and its unrefined/unprocessed products ensures nutrients and fibre are not removed from food. Its high fruit and vegetables content are packed with many nutrients, supply necessary fibre, vitamin and minerals, antioxidants, phytoestrogens and anti-inflammatory agents. They are protective against disease and decrease the risk of cardiovascular disease and obesity (Slavin & Lloyd, 2012).

Added sugar to a diet promotes weight gain, meta-analyses of randomised trials shows that added sugar also raises triglycerides and total cholesterol. Further to this it raises blood pressure, and increases the risk of cardiovascular disease (Ludwig, Hu, Tappy, & Brand-Miller, 2018). With the Palaeolithic diets no sugar intake reduces the risk factors of these diseases.

The cons include the meat consumed and its high fat content, as in the paleolithic era the meat was wild game, which is lean and contains less fat, along with fish and shellfish. However, the quantity of meat consumed today is higher than the recommended daily intake which presents a risk for chronic disease and certain cancers. The exclusion of legumes and wholegrains is also a concern due to the restriction of necessary nutrients (Harvard School of Public Health, 2019c).

Legumes include items such as peas, beans and lentils and are a part of a nutritional diet offering health benefits. These benefits include a decrease in LDL cholesterol, and a reduced risk of cardiovascular disease (Ludwig, Hu, Tappy, & Brand-Miller, 2018).

Wholegrains have shown a decrease in the risk of T2DM, coronary heart disease, ischaemic stroke, total cardiovascular disease, and certain cancers along with all-cause mortality (Ludwig, Hu, Tappy, & Brand-Miller, 2018).

Contamination of our water causes contaminants in our fish. These contaminants when consumed can build up in our body resulting in health problems (Washington State Department of Health, n.d.).

In summary, the palaeolithic diet has had little reliable research to be able to draw any conclusion to its health benefits. It is nutritionally deficient in calcium, B vitamins and vitamin D, and with the exclusion of legumes and wholegrains would further restrict this diet from necessary nutrients beneficial to health. The diet is low in carbohydrates from the plant foods selected, and high in fat content, though mainly unsaturated. It is also environmentally unsustainable for man to hunt enough wild game to support global needs.

Mediterranean Diet

The traditional Mediterranean diet is based on the foods consumed in Crete, Greece and Southern Italy in the mid-20th century. These food choices resulted in longevity and a decrease in certain cancers, coronary heart disease, and lifestyle related chronic disease. This diet meets nutritional requirements, has no dietary restrictions and is high in fibre (, n.d.b; Harvard School of Public Health, 2019b).

The pros of the Mediterranean diet is in its high content of fresh fruit and vegetables, resulting in a high fibre intake. It includes legumes, also meets nutritional requirements, is low in saturated fat, is disease protective – T2DM, metabolic syndrome, blood pressure, cognitive disease, certain cancers, obesity, all-cause mortality, and CVD. Its environmental impact is sustainable (Martinez-Lacoba, Pardo-Garcia, Amo-Saus, & Escribano-Sotos, 2018).

Its cons include refined grains, dairy, meat, red wine which increases risk of cardiovascular diseases, digestive diseases, liver disease and certain cancers; breast, and bowel (National Drug Research Institute, 2018). Olive oil is not cardioprotective and increases risk of obesity. A PREDIMED trial of three groups on differing forms of oils; added nuts, added olive oil, and a low-fat diet. The results showed olive oil to not be cardioprotective (Sala-Vila et al., 2014). This diet also has a high salt content and includes eggs which increase cholesterol and the risk of cardiovascular events. One 65g egg yolk contains more cholesterol than the recommended daily intake (David Spence, 2016, p. 21). Lecithin is an ingredient in egg yolks that once converted by intestinal bacteria and oxidized in the liver to TMAO is associated with vascular disease which increases the risk by 2.5-fold of a cardiovascular event (David Spence, 2016, p. 22).

In summary, the traditional Mediterranean diet included little unprocessed/unrefined foods however, today has seen the inclusion of refined white flour used in bread and pasta. In comparison to the Standard American Diet it is a healthy preference. It helps in the prevention of disease, is nutritionally adequate and is environmentally sustainable.

Vegan Diet

A vegan diet consists of plant-based products with the exclusion of all animal products, and products that contain animal. Vegan can be divided into 2 groups, those that are primarily animal activists and consume a highly refined diet, and those that are health conscious and consume a wholefood plant-based diet. A plant-based diet can provide all the protein, minerals and vitamins needed. Protein is available in legumes, tofu, nuts, seeds, and grains. Calcium is available in some tofu, soy drinks with added calcium, almonds, tahini and Asian greens. People can receive their iron requirements from legumes, firm tofu, tempeh, seeds, nuts, wholegrain cereals, kale, spinach, and green peas. As vitamin B12 is not plentiful in a vegan diet it therefore requires to be supplemented by foods fortified in Vit B12 or by a sun-lingual vitamin tablet (Health Direct, 2019).

The pros of a vegan diet are its proven health benefits to reduce the risk of chronic disease, no animal food products leaving it free of cholesterol, its high fruit and vegetable content, high in fibre, vitamins, minerals and antioxidants, low in saturated fat and its environmental impact is sustainable.

When looking at the cons of the vegan diet we have to divide the research into the two groups of vegan and wholefood plant-based diets. The vegan diet is high in salt, high in sugar, and high in its fat intake. It can be iron & vitamin B12 deficient if not educated to this type of diet. It is mainly refined/processed and includes alcohol. The wholefood plant-based diet has no cons to mention.

In summary, a vegan diet can supply all the nutrients required for good health and disease protection. The refined/processed diet presents with issues of increased saturated fats and refined products that may increase the risk of obesity and chronic disease therefore, products such as cake, chips etc. are best consumed as discretionary foods. Vitamin B12 must be supplemented in a carefully planned diet to ensure adequate intake. The vegan wholefood plant-based diet presents as the healthiest diet which is low in fat, nutritionally adequate, prevents disease, environmentally sustainable and is unprocessed/unrefined.


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