What is HbA1c? Your three-month sugar average and your plate
HbA1c gives an idea of your average blood sugar over the past two to three months. We explain what it shows, what it does not, and which eating habits can be linked to it.
One of the questions we hear most often in consultations goes like this: "My fasting sugar came back normal, but my doctor looked at my HbA1c and asked me to review my diet. Why are the two different?" It is a fair question, because these two tests measure the same thing on different time scales. In this article we explain, as general information, what HbA1c shows, when it can be misleading and which habits at the table can be linked to it. What your own result means is assessed by the physician who examines you; diagnosis and treatment are carried out by your doctor. What we offer here is a reading guide.
What exactly does HbA1c show?
Haemoglobin inside red blood cells binds permanently with the glucose circulating in the blood over time. The laboratory measures the share of haemoglobin that has bound glucose in this way and reports it as a percentage or in mmol/mol. Because red blood cells live for roughly three to four months, this share gives an idea of the average blood sugar level over about the past two to three months. The last few weeks weigh more heavily in that average: a holiday two months ago leaves less of a trace than last night's dinner, but it still counts.
Fasting blood sugar, on the other hand, is a snapshot of that particular morning. A plate of pasta eaten late the night before, a bad night's sleep or even a stressful morning can affect it. HbA1c is not much affected by the ups and downs of a single morning. That is why the two tests complement each other: one describes the moment, the other the longer trend. Doctors therefore often look at both together.
It also helps to know that HbA1c does not always reflect reality. Iron deficiency anaemia, haemoglobin differences such as thalassaemia trait, recent blood loss or transfusion, pregnancy and advanced kidney disease can change the lifespan of red blood cells or the structure of haemoglobin and make the result look higher or lower than it really is. In such cases your doctor may use other tests as well. Conclusions reached alone, such as "my HbA1c is this, so I am diabetic" or "my value is low, so there is no problem", are not sound.
How are the reference ranges read?
The classification used by the American Diabetes Association (ADA) for adults is the framework you will meet most often on laboratory reports. An HbA1c below 5.7% is considered the normal range. Between 5.7% and 6.4% is defined as prediabetes, a zone approaching the diabetes threshold. A value of 6.5% or above is one of the diagnostic criteria for diabetes; however, the diagnosis is not made on a single measurement but is confirmed by repeating the test, when there are no symptoms, or by another test. The same thresholds correspond to roughly 39 and 48 mmol/mol.
For people already diagnosed with diabetes, the conversation changes. Now we talk about a target, and that target differs from person to person. The ADA mentions below 7% as a general target for many non-pregnant adults, but for older people, those who often experience low blood sugar or those with other serious conditions, the doctor may set a more flexible goal. Your neighbour's target is not your target. You can find a detailed explanation of this parameter on the HbA1c page of our lab test guide; there, too, we give general information rather than personal interpretation.
Eating habits that can be linked to HbA1c
Diet is not the only factor affecting HbA1c; medication, physical activity, sleep, stress and genetic background are all part of the picture. Still, the plate is one of the areas a person has a say in every day. Below are the topics we focus on most in consultations.
Type and amount of carbohydrate
Cutting carbohydrates out completely is neither necessary nor sustainable for most people. What matters more is where they come from and how much is eaten. Bulgur pilaf instead of white rice, wholegrain or rye bread instead of white bread are higher-fibre choices. Pulses such as green and red lentils, chickpeas and white beans contain both fibre and plant protein and can help blood sugar rise more slowly. When a ladle of rice and a slice of bread are both added next to a plate of beans, however, the carbohydrate load climbs quickly; simply choosing one of the two makes a difference.
What sits next to the carbohydrate
The same carbohydrate behaves differently depending on what accompanies it. A seasonal salad, green beans or leeks cooked in olive oil, a bowl of yoghurt or cacık can slow the rate at which sugar from the plate passes into the blood. Some studies suggest that a simple order, salad and vegetables first, then protein, grains last, can soften the rise in sugar after a meal. We suggest it as a habit worth trying, not as a strict rule for everyone.
Drinks and the sugar in your tea
One or two sugar cubes dropped into each glass of tea through the day add up to a sizeable total that nobody counts by the evening. Fruit juices, bottled iced teas and fizzy drinks carry sugar unnoticed in the same way. Ayran, mineral water, unsweetened tea and water are plainer options. If giving up sugar in one day feels hard, going down to half a cube per glass first and taking the next step a few weeks later is a more realistic route.
The breakfast table
A breakfast where simit, pastries, jam and honey all meet on the same table means starting the day with a high sugar load. Instead of banning these foods, we talk about giving them a smaller place. For example, these swaps work for many people:
- One or two slices of wholegrain bread instead of a simit; if simit is eaten, half of one with plenty of greens.
- Boiled egg, white cheese or lor instead of jam and honey; a few slices of cinnamon apple if something sweet is wanted.
- Tomato, cucumber, pepper and parsley on the table every day.
- Olives and a handful of walnuts added to breakfast.
The meter at home and HbA1c are not the same
A finger-prick reading at home is a momentary value and does not replace HbA1c; HbA1c does not replace home readings either. Of two people with the same HbA1c, one may run along a smooth line all day while the other swings between very high and very low values. The average hides that swing. Your doctor may therefore suggest readings at different times of day or a continuous glucose monitor if needed.
Keeping home readings together with a food diary is one of the records that helps us most. Notes such as "this value two hours after lentil soup and bulgur pilaf, that value after the evening I had pide" show how general advice can be adapted to your daily life. When and how often to measure is best decided with your doctor.
What we do in a dietitian consultation
In the first meeting we look at your test results together, but this is not a diagnostic assessment; we work from the diagnosis and medication your doctor has given. We do not change your medication and we do not advise you to change it. What we do is build an eating pattern that fits your working hours, your family table and the dishes you like. With clients who fast during Ramadan, we also discuss how to set the iftar table and where pide and desserts fit in; the decision to fast should always be made with a doctor. You can read how we work in our nutrition in diabetes page.
If you would like to talk through your test results from a nutrition point of view, you can plan a consultation on our appointment page.
Frequently asked questions
Do I need to fast before an HbA1c test?
Because HbA1c reflects the average of the past two to three months, it usually does not require fasting. If other tests such as fasting glucose or cholesterol are ordered from the same blood sample, fasting may be needed; follow the instructions of your doctor and the laboratory.
My HbA1c is in the prediabetes range. What should I do?
First, talk to the doctor who ordered the test; they may repeat it or ask for other tests. In the prediabetes range, eating pattern, physical activity and weight management are usually the first topics discussed, and a dietitian can help you fit these steps into daily life.
How long after changing my diet will HbA1c show a difference?
Since HbA1c is an average of roughly two to three months, it takes time for a change to show; repeat testing is therefore usually planned at around three months. How much it changes differs from person to person, and it would not be right to give a number in advance.
