‘Prediabetes’ isn’t an official diagnosis or specific condition as such, it’s just a shorthand way of saying ‘at risk of diabetes’. It’s quite commonly used these days, and seems to have been imported from the US as a term.
As others have said the usual UK criteria for being considered ‘at risk’ is an HbA1c between 42-47mmol/mol. Two results at 48 or above are generally enough to give you a diagnosis with T2.
HbA1c measures how much excess glucose has been circulating in the bloodstream. When glucose cannot properly be absorbed and used by the body, it remains in the bloodstream and can affect red blood cells by sticking to them. Since red blood cells last approx 120 days, measuring the amount that have been ‘glycosylated’ gives an estimation of glucose concentrations in the blood over the past 3-4months.
Your reading of 49 or 50 suggests that your metabolism is beginning to struggle with balancing glucose absorption. The body mainly derives glucose from carbohydrates in the diet - both simple sugars, and also starches (longer chains of glucose molecules that are broken down in the gut).
Good luck with the weight loss! There are lots of different strategies you can use to try to lose excess weight (eg calorie restriction, low carb, meal replacement shakes). So it’s helpful to find one that suits you, your body, and your goals.
Let us know how you get on 🙂