Normal results are good news. But they're a snapshot, not the whole story. Here's what a CGM can show a healthy person, how to test foods on your first wear, and how long to wear one.
It's one of the most common questions I get about CGMs: "I feel fine, and my doctor says my blood tests are normal. Why would I need one?"
First, if your results are normal, that's wonderful news. Keep doing what you're doing. But "normal" doesn't always mean "optimal", and a health screening can only tell you so much. A continuous glucose monitor (CGM) fills in the gaps, and it's often the people who feel healthy who learn the most from it, because they're in the best position to act early.
Most health screenings in Singapore check fasting glucose and sometimes HbA1c. Fasting glucose is taken after 8 to 12 hours without food, which is usually the quietest point of your whole day. HbA1c is an average over roughly 3 months. Two people can have the same HbA1c, one with gentle, steady curves and the other with big spikes and dips that average out.
Neither test shows what happens in the hours after you eat, which is where most of us spend much of our waking day.
A Stanford study put CGMs on 57 adults, most of whom were considered normal on standard tests. Some of those "normal" people still spent up to 15% of their day in the prediabetes range. When everyone ate the same breakfast of cornflakes and milk, about 80% of participants went above 7.8 mmol/L, the level where after-meal glucose is considered raised.1
After-meal glucose matters. A large European analysis of more than 25,000 adults found that, even among people with normal fasting glucose, the risk of dying rose as their glucose 2 hours after a sugar drink went up. The authors concluded that fasting glucose alone does not identify everyone at risk.2
In a UK study that followed more than 6,500 adults, people who went on to develop Type 2 Diabetes had falling insulin sensitivity over the five years before diagnosis. Their fasting glucose only rose sharply in the last three years.3 In other words, by the time a standard test flags a problem, it has usually been building quietly for a long time.
A normal result tells you where you are today. A CGM helps you see where you're heading.
High spikes after ordinary meals, glucose that takes a long time to come back down, or a baseline that sits higher than you'd expect can all be early signs that your body is working harder than it should. Seeing them now, rather than in a diagnosis years later, gives you time to change course with simple habits.
Generic advice only goes so far, because people respond very differently to the same food. An Israeli study of 800 people found large differences in how individuals responded to identical meals.4 The PREDICT study of more than 1,000 adults, including identical twins, found that genes explained less than 10% of the differences in glucose response.5 Your meals, sleep, activity and timing matter far more, and those are all things you can change.
Oats, brown rice, wholemeal bread, fruit juice, smoothies and granola all have a healthy image. For some people they're fine. For others, they cause bigger spikes than the foods they were meant to replace. The only way to know is to test.
Rosalind had gained 7kg during COVID. She was eating clean and exercising, and even her doctor couldn't find the problem. Her CGM revealed hidden carbs quietly spiking her blood sugar. Once she could see them, she could manage them. She lost all 7kg and more.
Many people find that the afternoon slump, the 4pm snack craving or the heavy feeling after lunch lines up with a big spike followed by a drop. When you can see it, you can plan meals that keep your energy steadier.
Glucose isn't only about food. A short night, a stressful meeting, a late dinner, a glass of wine or a hard workout can all show up on your curve. These are often the most surprising lessons.
MOH has estimated that 1 in 3 people in Singapore has a lifetime risk of developing diabetes. If diabetes runs in your family, a CGM shows you how your own body is coping today, not just what your genes might predict.
For a first wear, one full sensor is usually enough. Most sensors last about 14 to 15 days, which gives you two useful phases:
Some people choose a second sensor straight away to test more foods or confirm that their changes are working. After that, I suggest a sensor every 3 to 6 months, or whenever something big changes: a new job or a stressful season, a new eating pattern or training plan, recovery from illness, or perimenopause and menopause. Each wear becomes a check-in on how your body is doing.
The simple Excel tracker I use with clients for their first sensor. Log your meals and readings, and it does the maths for you.
Open it in Excel, Google Sheets or Numbers. Start with the "Start Here" tab.
Download the tracker (.xlsx)A CGM is most useful when you treat it like a series of small, fair experiments. Here's the method I teach.
There's no official target for people without diabetes. In a study of healthy adults, glucose stayed between 3.9 and 7.8 mmol/L about 96% of the time.6 This is the practical guide I use with clients. It's not a diagnosis.
| What to check | What I'd like to see |
|---|---|
| Peak after a meal | Stays below 7.8 mmol/L |
| Rise from your starting number | A gentle hill, ideally less than 1.7 mmol/L |
| Back near your starting number | Within 1.0 mmol/L of your starting number by 2 hours, and within 0.5 mmol/L by 3 hours, without crashing below it |
| Overnight | A fairly steady line, without big climbs or drops |
| Test | Compare it with |
|---|---|
| Kaya toast with kopi | The same, with the two soft-boiled eggs eaten first |
| Your usual oats or cereal | Steel-cut oats instead of instant, or eggs and vegetables instead |
| Chicken rice | Half the rice, with a plate of vegetables and the chicken eaten first, plus a braised egg for extra protein and healthy fats |
| Kopi or teh | Siew dai, then kosong |
| Fruit juice or a smoothie | The same fruit eaten whole |
| Bubble tea | 0% or 25% sugar, with or without toppings |
| Dessert on its own | The same dessert straight after a meal, then followed by a 10-minute brisk walk |
Write down what you ate, when, and anything unusual (poor sleep, stress, exercise) in your CGM app. After two weeks, those notes are what turn a squiggly line into real insight.
In 2022, my HbA1c was 9.7%. By October 2023, it was 5.1%, and I was 16kg lighter. My CGM was my daily teacher through that journey. It's why I now encourage people to look at their curve while they still feel fine. It's so much easier to adjust early than to reverse a diagnosis later.
Normal blood work is worth celebrating. But it's a snapshot taken at your calmest moment. Two weeks with a CGM shows you how your body handles real life: your meals, your sleep, your stress and your movement. For a healthy person, that's not a reason to worry. It's a chance to stay healthy on purpose.
I'm May, a breast cancer survivor who reversed my Type 2 Diabetes with the help of a CGM. I now coach people in Singapore to understand their blood sugar and build habits that last.
Work with meJoin a CGM workshopThis article is for education only and is not medical advice. Please speak with your doctor before making major changes to your diet, exercise or medication, especially if you have a pre-existing medical condition.
