By Marie Spano, M.S., R.D., Contributing Editor
From the Atkins diet to some forms of the Paleo diet, high-protein diets are common for weight loss. Such diets restrict carbohydrate intake so the body goes into ketosis, a metabolic state where it burns its own fat for fuel. How effective are these and what are the parameters?
Ketosis is achieved by limiting carbohydrate intake, resulting in decreased glucose availability, favoring fatty-acid oxidation. Fat is converted into fatty acids and ketone bodies, leading to increased blood ketones that serve as a fuel source for cells that cannot use fatty acids for energy. As an alternate fuel source, ketones attenuate muscle-tissue breakdown for energy production (Cleveland Clinical Journal of Medicine, 2002; 69:849-962; Nutrition and Traumatic Brain Injury, National Academies Press, 2011).
A ketogenic diet is one that is low in carbohydrate, though there is no universal standard for the carbohydrate, protein or fat content. However, studies have outlined varying amounts of carbohydrate to induce ketosis. One residential study in obese men used an ad libitum diet containing 4% carbohydrate, 66% protein and 30% fat, which induced ketosis after one to three days (American Journal of Clinical Nutrition, 2008; 87:44-55). Other researchers defined a low-carbohydrate ketogenic diet as one containing a maximum of 50 grams of carbohydrate per day regardless of fat and protein content (Current Atherosclerosis Reports, 2003; S:476-483). And, the traditional ketogenic diet, used as a treatment for pediatric epilepsy, is described as one that contains a fat-to-protein ratio of 4:1. Overall, studies and clinical experience suggest there is a maximum dietary carbohydrate threshold of 65 to 180 grams per day to initiate lipolysis and ketosis (American Journal of Physiology, 1992; 262:E631-E636).
Low-carbohydrate ketogenic diets are a viable dietary approach to obesity because ketosis can decrease hunger levels and subsequent calorie intake (American Journal of Clinical Nutrition, 2008; 87:44-55). In addition, a traditional ketogenic diet, marked by its high fat content and reduced carbohydrate and protein content, reduces serum insulin levels, leading to a low insulin/glucagon ratio and lipolysis. Finally, studies show low-carbohydrate ketogenic diets decrease fasting blood glucose levels, blood triglycerides and high-density lipoprotein (HDL) cholesterol in obese adults (Current Atherosclerosis Reports, 2003; S:476-483; American Journal of Clinical Nutrition, 2008; 87:44-55).
Because ketogenic diets are low in carbohydrate, they may fall short on fiber, vitamins A, C and E, thiamin, folic acid, iron, calcium and magnesium (Cleveland Clinic Journal of Medicine, 2002; 69:849-862; American Journal of Clinical Nutrition, 2010; 92:304-312; The American Journal of Cardiology, 2001; 88:59-61). However, to date, most studies on low-carbohydrate diets, including low-carbohydrate ketogenic diets, have included a multivitamin. In addition, some have also included sodium and potassium supplements (American Journal of Clinical Nutrition, 2007;8 6:276-284).
And though research suggests that ketogenic diets are safe in the short term, they should be followed only under medical supervision (The New England Journal of Medicine, 2008; 359:221-241).