If you cut carbs, walk every day, lost real weight, and your fasting glucose or A1c still has not budged, the most likely explanation is not that you failed. It is that the number you are watching is slow, noisy, and influenced by things that have nothing to do with your diet: sleep, stress hormones, the timing of your test, how fast your body burns through its overnight fuel, and in the case of A1c, the lifespan of your red blood cells. A single reading that went the wrong way is not a verdict on months of work.
That said, "you did nothing wrong" is a lousy place to stop. There are usually two or three specific levers still sitting untouched. This post walks through the ones that come up most often.
Why did my A1c go up even though I lost weight?
This is one of the most common and most demoralising things people describe to us. One person wrote in after losing 11kg and watching their A1c climb from 4.9 to 5.9 over the same stretch. Nothing about that is a reward for the effort.
A few things can produce that pattern:
- A1c is an average over roughly three months, so it lags behind what you changed. A reading taken today partly reflects a version of you from twelve weeks ago.
- A1c reflects how long your red blood cells have been circulating. Anything that lengthens their lifespan, including low iron status, can push the number up without your glucose actually being worse. Anything that shortens it can push the number down. This is worth raising with your doctor rather than guessing at.
- Rapid weight loss is itself a stressor. Cortisol tends to rise when the body is under an energy deficit, poor sleep, or hard training, and cortisol raises glucose. Some people see their numbers drift up during the losing phase and settle afterwards.
- The scale and the metabolism are not the same measurement. You can lose weight while insulin resistance stays roughly where it was, especially if the weight came off mostly through eating less rather than through changing what insulin has to respond to.
If your A1c moves in a direction that makes no sense against how you feel and how you are eating, get it repeated, and ask for a fasting insulin alongside it.
Why is my fasting glucose still over 100 when I walk 12,000 steps a day?
Fasting glucose is the single most misread number in metabolic health. It is measured at the exact moment your body is doing the most work to keep you fuelled: the end of an overnight fast, when cortisol and growth hormone are rising to wake you up and your liver is releasing stored glucose on purpose. That morning rise, often called the dawn phenomenon, is a normal signal, not a diet failure.
Walking 12,000 steps a day is genuinely doing something. Muscle contraction moves glucose out of the blood through a pathway that does not require insulin, which is exactly the kind of help you want. But that effect is strongest in the hours around the walk. If all your steps happen at 7am and your largest meal lands at 8pm, the two are not meeting each other.
Practical adjustments worth testing:
- Move 10 to 15 minutes of your existing walk to the 20 minutes after your biggest meal instead of before breakfast. Same effort, different timing.
- Add resistance work twice a week. More muscle means more storage capacity for glucose, which may matter more over months than step count does.
- Check what time you last ate. Eating late and testing early tends to produce a higher morning reading than eating earlier and testing at the same time.
Am I tracking the wrong marker entirely?
Often, yes. Fasting glucose is what your body has managed to achieve. Fasting insulin is how hard it had to work to achieve it. Insulin resistance can build for a long time while glucose stays acceptable, because rising insulin is holding the line. By the time fasting glucose starts drifting, a lot has already happened upstream.
If you are doing everything right and the glucose number will not move, ask your doctor for:
- Fasting insulin, ideally drawn at the same time as fasting glucose
- HOMA-IR, which is calculated from those two together
- Triglycerides and HDL, since their ratio often shifts before glucose does
People sometimes find that fasting glucose has stayed flat while fasting insulin has come down meaningfully. That is progress you could not see before, and it changes how you feel about the last six months.
Can low carb itself raise my fasting glucose?
It can, and this catches a lot of careful people out. When you have been eating very few carbohydrates for a while, muscle tissue becomes more willing to run on fat and more reluctant to take up glucose, which helps keep glucose available for the brain. Some people call this adaptive or physiological insulin resistance. The result can be a fasting glucose that looks worse on paper while post-meal readings and overall control look fine.
Two ways to tell the difference between this and a real problem:
- Look at your post-meal numbers, not just your morning one. If glucose returns close to baseline within two hours of eating, the picture is not the same as a stuck fasting number on its own suggests.
- Look at fasting insulin. Adaptive glucose sparing tends to come with low insulin. Genuine insulin resistance tends to come with high insulin.
This is a conversation to have with your doctor rather than a reason to abandon an approach that is otherwise working for you.
What is usually still hiding in a "clean" low-carb diet?
When someone tells us they have cut carbs and nothing changed, there are a handful of things that keep turning up when we look at the actual plate. None of them are moral failures. They are just leaks.
- Liquid calories. Juice, smoothies, sweetened coffee drinks and alcohol hit the bloodstream fast because there is nothing to slow them down. A smoothie made of whole fruit still behaves very differently from the fruit.
- Low-carb ultra-processed food. Protein bars, keto snacks, flavoured yoghurts and diet desserts. The label is technically low carb. The processing level, sweeteners and fat quality can still drive an insulin response you did not plan for.
- Food order. Eating vegetables and protein before the starchy part of a meal tends to blunt the glucose rise compared with eating the same food in the opposite order. It costs nothing and requires no removals.
- Not enough fibre. Cutting carbs often means cutting the fibre that came with them. Fibre is one of the strongest moderating factors on how a meal lands.
- Sleep. Short or broken sleep tends to raise next-day glucose and appetite regardless of what you eat. If you are averaging five hours, that is the lever, not the salad.
This is the logic behind the Insulin Fix score. It runs from 0 to 100, and a higher score means a lower insulin load. It weighs glycemic load, protein, fibre, processing level, fat quality, liquid calories and food order together, because a food that looks fine on one of those can still be working against you on three others.
What should I change first if I have already done the obvious things?
Pick one, run it for three to four weeks, and keep everything else the same so you can actually read the result.
- Move your walk to after your biggest meal. No extra time required.
- Eat protein and vegetables first at every meal for a month. Do not remove anything.
- Cut liquid calories to zero, including alcohol, for four weeks. This is often the fastest single change.
- Swap two low-carb packaged products for real food, for example a protein bar for eggs, or flavoured yoghurt for plain yoghurt with berries and nuts.
- Add two resistance sessions a week. Twenty minutes counts.
- Protect sleep for a month before changing anything else about your food.
Then retest, with fasting insulin included this time. And keep the 80/20 principle in mind: an approach you can hold for a year beats a perfect one you abandon in five weeks, and the stress of white-knuckling a rigid plan is not neutral for your glucose either.
When is it time to stop self-managing this?
If you have genuinely changed your food, movement and sleep for three months and your numbers have not moved or have worsened, that is a reason to get a fuller workup rather than to try harder. Thyroid function, medications including steroids and some blood pressure drugs, iron status, sleep apnea, perimenopause and PCOS can all affect these markers, and none of them respond to another round of dietary discipline. Bring your actual data to the appointment: dates, readings, what you changed and when.
Frequently asked questions
Is a fasting glucose of 100 to 105 something to worry about?
It sits at the lower edge of the range clinicians call impaired fasting glucose, so it is worth watching and worth discussing, but a single reading is not a diagnosis. Morning readings are influenced by sleep, stress and the natural dawn rise in hormones. Ask for a repeat test plus fasting insulin and A1c before drawing conclusions.
How long should it take for A1c to reflect changes I have made?
A1c reflects roughly the previous three months, so retesting at six or eight weeks will mostly show you your old self. Twelve weeks is a fairer interval.
I lost weight but my metabolic numbers got worse. Should I stop losing weight?
Not necessarily, but it is worth asking whether the rate is too aggressive and whether sleep and stress are taking the hit. Weight loss that comes with chronic under-fuelling and poor sleep can raise cortisol, and cortisol raises glucose. Slowing down, eating enough protein and sleeping more may do more for the numbers than cutting further.
Do I need a continuous glucose monitor to figure this out?
You do not need one, but it can be useful for a few weeks if you want to see how specific meals and the order you eat them in actually land for you. The insight most people get from it is that individual responses vary more than any general food list can capture.