Can leucine affect your blood sugar or insulin?
Leucine prompts the pancreas to produce insulin. Your blood sugar only falls as a result if carbohydrates are also present. High leucine levels in the blood are more likely a signal of an already disrupted metabolism than the cause of it.
Leucine on its own, as a single amino acid, triggers a measurable release of insulin, but does not lower your blood sugar as a result. That comes down to how insulin works: it needs glucose to produce its blood-sugar-lowering effect. Take leucine together with carbohydrates, however, and the two reinforce each other: the insulin response is greater than you would expect from either one alone, and the blood sugar spike after a meal is reduced.
In people with type 2 diabetes or severe excess weight, researchers see the same pattern: both eating leucine and delivering it directly into the bloodstream stimulate insulin release and can lower blood sugar. How large this effect is in practice varies from person to person and situation to situation.
High levels of leucine in the blood are clearly linked to a higher risk of insulin resistance (where your cells respond less well to insulin) and type 2 diabetes. But which comes first? A large genetic study involving around 250,000 people shows that high leucine levels are more likely the result of excess weight and poor insulin function than the cause of them. High leucine levels may, however, independently contribute to unfavourable blood fats, such as higher triglycerides (a type of fat in the blood) and lower-quality cholesterol.
Genetic analyses also point to a possible vicious cycle: people who break down leucine poorly are more likely to have disrupted insulin function, and in turn the breakdown process works less well when insulin function is already impaired. How much leucine you take in through your daily diet is linked to insulin resistance in only one of the three studies available; the other two find no connection. No conclusions can yet be drawn from this.
Pregnant women with higher leucine levels in their blood are found more often to have gestational diabetes in an analysis of 28 studies, but again this is an association and not a proven cause. If you are pregnant and concerned about your blood sugar, discuss this with your midwife or doctor.
This answer draws on several comprehensive overviews of existing research, two large analyses combining multiple studies, a genetic study involving around 250,000 people, and one small study in 15 healthy men. The evidence on leucine's direct insulin-stimulating effect is reasonably consistent. The question of whether high blood leucine levels are a cause or a consequence of insulin resistance has been answered fairly concretely by the large genetic study: consequence, not cause. The evidence on dietary leucine intake and insulin resistance is contradictory and too limited to draw conclusions from.
Does stress raise your blood sugar when you eat carbohydrates?
Stress raises blood sugar through stress hormones. Eating carbohydrates on top of that likely amplifies the rise, because the body is less able to process glucose at that moment.
Does taking glutathione supplements make sense, or is it broken down in your gut?
Standard glutathione tablets are largely broken down before they reach your bloodstream. Newer formats such as liposomal or under-the-tongue dissolvable varieties achieve higher blood levels.