The Study

Alessandro et al. (2015) studied the effects of a 20-day ketogenic diet (KD) on weight loss, metabolism and respiratory parameters using overweight healthy people as subjects. It is interesting to note that it was one of the first studies to investigate the respiratory effects of a KD.


Thirty-two overweight Italian adult female subjects were recruited to participate in this study. Chosen subjects had a normal diet with high level of carbohydrates (more than 55%) and were considered as healthy with no major health problems such as renal malfunction or diabetes. Furthermore, pregnant or breastfeeding women, as well as subjects that have recently changed their habits, like the ones taking a new drug or undergoing a new exercise program, were excluded from the study. The selected subjects were then divided in two groups. The first group implemented a KD for 20 days (14% carbohydrates, 43% fats and 43% protein) followed by 20 days of a low-carbohydrate non-KD (34% carbohydrates, 39% fats and 27% protein). During this period, the group also consumed many different plant extracts. The second group implemented a Mediterranean diet (60% carbohydrates, 25% fats and 15% protein) with 1200 kcal/day for the first 20 days and 1400 kcal/day for the next 20 days. After that initial period, both groups were on a 1400 kcal/day Mediterranean diet for the next 2 months. Body parameters were measured at the beginning of the study, after both periods of 20 days and after the last 2-month period.


Both diets helped people to significantly lose weight, particularly in the first part of the study, but subjects with the KD lost a greater percentage of body fat than the ones with the Mediterranean diet. For the KD group, there was a significant decreased in some respiratory parameters, such as the respiratory exchange ratio (RER), the carbon dioxide output and the carbon dioxide end-tidal partial pressure (PETCO2), while other parameters, such as the oxygen uptake (VO2), the carbon dioxide production (VCO2) and the resting energy expenditure (REE), remained unchanged. There were no significant differences for those respiratory parameters in the Mediterranean diet group. These changes in respiratory parameters observed in the KD group are consistent with metabolic changes required to burn fat instead of carbohydrates as the major source of energy for the body. Furthermore, these results also suggest that KD significantly decreased the storage of carbon dioxide within the body.


The authors concluded that short-term KD might be useful for weight loss, as well as for decreasing the total percentage of body fat. The results also suggest that KD might theoretically be useful for patients suffering from illnesses characterized by an increase of carbon dioxide arterial partial pressure caused by respiratory insufficiency or failure. However, this is actually just a hypothesis and the authors stressed the fact that more studies will be required to assess the real potential of KD for these respiratory illness cases.

Study Editor

Marie-Christine Brotherton holds a Ph.D. in Cellular and Molecular Biology with specific expertise in Parasitology, Proteomics, Drug Resistance and Genomics. She also holds a MBA with a major in Corporate Social and Environmental Responsibility. She has strong experience with the scientific publication process, including author guidelines requirements, as well as with the medical and social/environmental fields. She can be reached by email at


Alessandro, R., Gerardo, B., Alessandra, L., Lorenzo, C., Andrea, P., Keith, G., … & Antonio, P. (2015). Effects of Twenty Days of the Ketogenic Diet on Metabolic and Respiratory Parameters in Healthy Subjects. Lung193(6), 939-945.