Your A1c came back high.Here's what moves it.

A1c is the percentage of your red blood cells that have sugar attached to their hemoglobin. Red blood cells live about three months, so the number reflects your average blood sugar over the past two to three months.

The cutoffs the CDC, NIDDK, and MedlinePlus all use:

• Below 5.7%: normal
• 5.7% to 6.4%: prediabetes
• 6.5% or above: diabetes

For most people with diabetes, the ADA's target is 7% or less and NIDDK's is below 7%. It is individual: NIDDK says people with other health conditions may be given a less strict target, 7% to 8% or higher. Under the A1c sit the day-to-day numbers NIDDK lists, 80 to 130 mg/dL before a meal and under 180 about two hours after one starts, and those can differ by age and health too. Your target is the one your doctor gave you.

With diabetes, A1c is tested at least twice a year, and the ADA says more often if your treatment plan has changed or isn't working as expected. With prediabetes, the CDC says every one to two years.

Because the test averages roughly three months, a change you make today shows up in a number measured over the following months. None of the sources give a faster clock than that, so this page doesn't either.

In the Look AHEAD trial, adults with type 2 diabetes in an intensive lifestyle program lost an average of 8.6% of their body weight in a year, and their average A1c went from 7.3% to 6.6%. The comparison group went from 7.3% to 7.2%.

For prediabetes, NIDDK says losing 5 to 7 percent of your starting weight may prevent or delay type 2 diabetes. Separately, the CDC reports that people with prediabetes who joined a structured lifestyle change program cut their risk of developing type 2 diabetes by 58%, and by 71% for people over 60.

The CDC and NIDDK guideline is at least 150 minutes a week of moderate activity, such as brisk walking, plus muscle-strengthening on two days. NIDDK also phrases it as 30 minutes on five days.

The walk after dinner has its own evidence. In one small study of older adults at risk for high blood sugar, 15-minute walks starting 30 minutes after each meal lowered blood sugar after dinner more than a single 45-minute walk did. That study measured after-meal blood sugar over two days. It says nothing about A1c over months, so take it as a reason the timing matters and nothing more.

• Fiber. Your body doesn't absorb it, so it doesn't spike blood sugar the way other carbohydrates can. The CDC cites the Dietary Guidelines' 22 to 34 grams a day, depending on age and sex, from foods like oats, beans, lentils, brown rice, apples, pears, broccoli, nuts, and seeds.
• Sugary drinks. A 12-ounce regular soda has about 42 grams of added sugar, around 150 calories, and the CDC lists type 2 diabetes among the problems adults who often drink them are more likely to have. Sports drinks, energy drinks, fruit drinks, and sweetened waters count.
• The pattern. The NHS advice is fruit, vegetables, wholegrain foods like wholemeal bread and oats, and pulses, and less of the processed food with lots of salt and sugar. Its other line is worth keeping: a small change every week makes it easier.

The CDC's diabetes guidance explains the mechanism: when you regularly don't get enough sleep, you may have less insulin to balance your blood sugar and more cortisol, which makes it harder for insulin to do its job. Short sleep also raises the hunger hormone and lowers the fullness ones, which is why a bad night tends to become a bad day of eating.

NIDDK's instruction is to take your medicines as prescribed even if you feel good or have reached your goal. For metformin, MedlinePlus says it controls diabetes but doesn't cure it, so keep taking it even when you feel well, never more or less than prescribed, and don't stop without talking to your doctor. If cost is why doses get skipped, NIDDK says to raise it with the care team rather than ration.

• Don't stop or change a diabetes medicine unless your prescriber tells you to.
• Don't switch to a very strict, low-calorie diet without talking to a health professional first. The NHS warns it can interact with insulin and other diabetes medicines.
• If you're vomiting, have diarrhea, or a high fever while on diabetes medicine, get urgent medical advice before adjusting anything yourself.

I never adjust a medication, never diagnose, and never set your target. What I do is ask every day about the things your doctor named, the walk, the soda, the pill, keep the fasting readings you text me with their dates, and read them back before the retest so the visit starts with the record.

No clinician reviewed this page. It restates the CDC, NIDDK, ADA, NHS, and MedlinePlus pages and the two studies linked below, and those are the documents to trust over anything here.