Despite an impressive capacity to induce diabetes remissions, the gastric bypass surgery has been associated with the onset of hyperglycemic peaks, which are very intensive and transient, in formally non diabetic patients. The aim of this study is to study the digestion of starch as compared to that of glucose (same glucose load) before and after gastric bypass surgery in obese patients.

Volunteers will be recruited among the candidates to a gastric bypass, and will be studied before and 3 months after surgery. They will have on each occasion 2 random meals, corresponding to 30g glucose, one made of starch the other made of glucose, both naturally labeled with 13C. The digestion of starch will be assessed with the increase in the plasma 13C-glucose tracer. Plasma samples will be collected for 3 hours.

Some studies have already investigated time of absorption of glucose, but any study has examined the time of digestion of glucose. Other study always used glucose syrup, so they cannot have results about digestion. It is the reason why, in this study, glucose syrup and a starch meal will be taken by the same patient and glycaemia will be compared. In this way, results will be obtained about the kinetic of digestion of starch.

Despite an impressive capacity to induce diabetes remissions, the gastric bypass surgery has been associated with the onset of hyperglycemic peaks, which are very intensive and transient, in formally non diabetic patients. The aim of this study is to study the digestion of starch as compared to that of glucose (same glucose load) before and after gastric bypass surgery in obese patients.

Volunteers will be recruited among the candidates to a gastric bypass, and will be studied before and 3 months after surgery. They will have on each occasion 2 random meals, corresponding to 30g glucose, one made of starch the other made of glucose, both naturally labeled with 13C. The digestion of starch will be assessed with the increase in the plasma 13C-glucose tracer. Plasma samples will be collected for 3 hours.

Some studies have already investigated time of absorption of glucose, but any study has examined the time of digestion of glucose. Other study always used glucose syrup, so they cannot have results about digestion. It is the reason why, in this study, glucose syrup and a starch meal will be taken by the same patient and glycaemia will be compared. In this way, results will be obtained about the kinetic of digestion of starch.

All patients will have two evaluations: one before the bypass surgery and one 3 months after. All evaluation will include 2 standard meals. Patients have to be fasted, and they will take in a randomized order the same glucose quantity: 30g, for the breakfast. After each meal, blood sample will be collected during 3 hours at time 0, 10, 20, 30, 40, 50, 60 minutes and every 30 minutes until time 180.

The starch meal will provide 30g of glucose in the form of corn starch. It will be consumed in 15 minutes. They are any other food in the meal. This quantity is corresponding to what patients can ingest after a bypass surgery, because of the poor size of their stomach. C13-carbon is a natural tracer into the corn. The measure of the increase of C13-glucose in the plasma is showing the appearance of the tracer, corresponding to the starch digestion.

The second meal is composed by 30g of corn glucose (glucose-meal), in liquid form and will be dived in 3 portions to be ingested in 15 minutes, like the starch meal. They are any other food in the meal.

Inclusion Criteria:

• Obese patients before obesity-surgery (HAS 2009 criteria for obesity-surgery)
• Patients accepted for a gastric bypass
• Patient consent the principle of 2 evaluations (one before surgery and another 3 months after surgery)
• Patient that give their informed consent before any procedure for the study
• Patient affiliated with a health insurance scheme

Exclusion Criteria:

• Diabetes (whatever the treatment), post-surgery diarrhea, small intestine disease
• Known microbial outbreak
• Anti-thrombin therapy
• Treatment which can modify the intestinal transit (anti-diarrhea, thyroid hormones…)
• Pregnant woman or breastfeeding.
• Patient not available for the two evaluations
• Protected adults (guardianship by court order)
• Patients participating to another treatment research protocol during the time of this study