The Ketogenic Diet: Healthy or Harmful?

www.tcd.ie/tsmj 39 With obesity on the rise in the western world, there is increasingly strong medical and social pressure to lose weight. There is a vast array of diet plans and products that take advantage of this pressure; many of which have little scientific basis for their claims. Most diets fall under the three general categories of “do-it-yourself”, non-clinical, and clinical regimes. Do-it-yourself diets rely on the motivation of the dieter and his or her willingness to investigate different options. These regimes usually employ diet books, special-purpose food products, and videos. The ketogenic Atkins diet is an example of this type of approach to weight loss. Non-clinical programs involve trained counselors who provide an educational and support service for clients, often after consultation with a health professional. Weight Watchers is a familiar example of a non-clinical program. Clinical programs involve direct interaction with health care professionals; often a group of specialists with training in nutrition, behaviour therapy, exercise, and counseling1. The goal of any diet is to maximise fat loss and minimise lean muscle breakdown. There is experimental evidence that ketogenic diets (a recently re-popularised group of weight loss regimes) are effective in reducing body fat, while maintaining lean muscle mass (see Figure 1). The cornerstone of any ketogenic diet (socalled due to the production of ketones during lipolysis) involves the ingestion of significantly reduced amounts of complex carbohydrates, such as those found in pasta, rice, bread, and potatoes3. In place of these, diets rich in protein from foods such as meat, fish, and dairy as well as green leafy vegetables are recommended. A typical daily menu is given to illustrate what may be consumed on such a diet (see Figure 2). The ketogenic diet has been shown to minimise muscle loss during dieting while maintaining a steady loss of body fat stores2. This type of diet also allows for rapid weight loss, as demonstrated by one study in which patients were shown to lose 1822kg in 12-15 weeks4. The ketogenic diet has also been utilised for applications outside of weight loss, including nutritional therapy for diabetics and for decreasing seizure frequency in children with medically refractory epilepsy5. Several examples of ketogenic diets include the currently popular Atkins Diet, the Banting Diet (introduced more than a century ago) and the Sippy diet (used for ulcer therapy)6. The physiological basis of the ketogenic diet relies on the reduction of insulin levels. Insulin is released in response to rising blood glucose. In the absence of glucose (either from digested carbohydrate or glycogen stores) certain hormonal changes occur leading to the use of stored fat for energy. When blood glucose decreases (<3.58mmol/L), growth hormone, epinephrine, and glucagon are released to maintain energy metabolism. Within the adipocyte, growth hormone and epinephrine activate the breakdown of triacylglycerol to fatty acids, which are transported to the liver and muscle. The oxidation of free fatty acids gives rise to acetyl-CoA, which can enter the Krebs cycle directly. However, in the liver, excess acetyl-CoA derived from fatty acid oxidation is converted to ketone bodies; namely acetoacetate, gamma-hydroxybutyrate, and acetone. This conversion occurs only in the liver, and the resultant ketone bodies are transported to peripheral tissues (such as muscle and brain) where they are converted back to acetyl-CoA for entry into the The Ketogenic Diet: Healthy or Harmful? A Review In Light Of Its Renewed Popularity Ann Pittier, 5th Year Medicine; Frank Corrigan, 5th Year Medicine