In a study of 143 patients fructose malabsorption was found in 45.8% of patients. Lactose intolerance was found in 20.3%. Both can be measured via a simple hydrogen breath test. 25 grams of fructose or lactose is administered to a fasting patient. Breath hydrogen levels are measured before administration and at 30 minute intervals for 3.5 hours. Sugar malabsorption contributes to intestinal dysbiosis, among other issues. Fructose malabsorption is treated with a fructose poor diet, while lactose intolerance is treated with a lactose free diet. A high baseline hydrogen breath measurement indicates intestinal bacterial overgrowth. Clinicians can buy the equipment to do the fructose and lactose breath testing in their offices. Prof De Meirleir believes these intolerances were present before the illness onset, acting as a predisposing factor and may also get worse after illness onset. He observes these issues are often present in family members.