Are Carbs Really Bad for You? The Science Behind Low-GI Foods, Whole Grains, and Blood Sugar
Updated: Aug 27
Smart Health Key 4/12 – Choose Smarter Carbs
If you've ever been told that carbohydrates are making you fat, causing blood sugar problems, or ruining your health, you're not alone.
Maybe you've tried cutting out bread, pasta, or rice. Maybe you've followed a low-carb diet and felt great for a while—only to find yourself desperately craving bread, sweets or baked goods a few days or weeks later.
Here's the thing:
You don't need to fear carbs. You need to choose them more intelligently. Carbohydrates are an essential part of a balanced diet.
✨The key is to choose mostly slow-digesting carbohydrates and whole grains, with the right type and amount depending on your activity level and when you're eating them.
This is where the Glycemic Index (GI) and Glycemic Load (GL) per serving become incredibly useful.
They help you understand how quickly different carbohydrate foods are digested and absorbed—and, ultimately, how they affect your blood glucose levels. Because not all carbohydrates behave the same way in your body and not all bread is created equal.
Whole grains: the smarter carbohydrate choice
Whole grains are an important part of a healthy diet. They contain the three main parts of the original grain:
The bran – the fibre-rich outer layer
The endosperm – the starchy part
The germ – the nutrient-rich part containing protein, vitamins, minerals and beneficial plant compounds
When grains are refined, much of the bran and germ is removed. This means losing significant amounts of fibre, vitamins, minerals and phytonutrients—and often results in a higher GI.
Whole grains, on the other hand, provide a range of nutrients and different types of fibre, as well as plant sterols, antioxidants and phytochemicals.
They also have prebiotic effects, meaning they can help support the beneficial bacteria living in your gut, as fibre is their food. And when your gut bacteria are happy, your whole body benefits too. The friendly microbes in your gut and the compounds they produce can help support healthy digestion, immune function and the body's response to inflammation and oxidative stress.
Whole grains have also been associated with benefits for heart health, blood pressure, cholesterol, insulin sensitivity and blood glucose control.
And here's another interesting thing:
The world's longest-living populations—the Blue Zone communities—eat plenty of whole grains as part of their traditional diets. That's not an accident we're willing to ignore.
What counts as a whole grain?
Whole grains include foods made from grains such as:
Barley
Brown and wild rice
Corn on the cob/whole corn or mealies)
Oats
Rye
Sorghum
Wheat ("stampkoring")
They can be eaten whole, cracked, rolled, flaked or ground, as long as the bran, endosperm and germ remain in the same relative proportions as the original grain. That means foods like rolled oats, some whole-grain breakfast cereals, bran-based cereals and certain mueslis can all contribute to your whole-grain intake. We actually need 3 portions whole grains/day to keep cholesterol in check.
One important point, though: "Whole grain" doesn't automatically mean "low GI."
The way a food is processed can affect how quickly it is digested. An intact whole grain will generally be digested more slowly than a finely ground whole-grain flour - thus whole wheat, barley, rye, sorghum, oats, corn are all low GI, except for millet, which is inherently high GI. There are also pseudo grains that are low GI, especially when intact, e.g. buckwheat and quinoa.
So, when choosing your carbohydrates, it's worth considering both the quality of the grain and how quickly your body can digest it.
Not all carbs are created equal
Here's where things get interesting. Two foods can both be classified as "carbohydrates" but have completely different effects on your blood glucose levels.
Compare a bowl of bean soup with a spoonful of icing sugar. Both contain carbohydrates. But they're clearly not the same thing.
The same applies to bread. A soft, highly refined white loaf can be digested much faster than a denser bread made with rye, oats, barley, seeds, legumes or intact whole grains.
The size of the food particles, the amount and type of fibre, the presence of protein and fat, and how the food is processed can all influence how quickly the carbohydrate is digested and absorbed.
In general:
The slower the digestion and absorption, the slower the rise in blood glucose.
That's why we generally recommend choosing slow-digesting, lower-GI carbohydrates for everyday meals.
What is the Glycemic Index (GI)?
The Glycemic Index (GI) is a scientific tool developed in the 1980s by Canadian scientists David Jenkins and Thomas Wolever. It measures how quickly the carbohydrate in a food raises blood glucose compared with a reference food. However, German scientists already started to study the effect of different carbohydrate foods on blood sugar levels as early as the 1930s and found that not all carbs were created equal!
Over the past several decades, researchers have measured the GI of thousands of foods in human subjects. The result? We now know that different carbohydrate foods can have dramatically different effects on blood glucose.
Generally, lower-GI foods are digested and absorbed more slowly (slower carbs).
Higher-GI foods are digested and absorbed more quickly (faster carbs).
And this matters because a rapid rise in blood glucose can be followed by a rapid fall—leaving you feeling tired, unfocused and looking for your next energy hit. This is due to an over-secretion of insulin, which is also a fat storer.
You know that feeling... You've had your breakfast... You felt fine for a while.
Then suddenly it's 10:30 am, and you're staring into your colleague's biscuit tin wondering if anyone would notice if you ate the whole thing.
That's the kind of energy rollercoaster we're trying to avoid.
The goal of a GI Smart way of eating is to choose slower carbs when you're inactive or going about your normal day, helping you maintain more stable blood glucose and energy levels, so that a fruit in-between your meals is sufficient.
What makes a carbohydrate food lower GI?
Several factors affect how quickly a carbohydrate is digested.
1. The size of the food particles
Generally, more finely processed foods are digested faster. That's one reason why a bread made from highly refined flour may be digested more quickly than a dense bread containing intact grains, legumes or seeds.
2. Fibre
Fibre can slow down digestion and absorption. Soluble fibre, found in foods such as oats, barley and legumes, is particularly effective at slowing the rate at which food leaves the stomach and enters the bloodstream.
3. Protein and fat
When protein and fat occur naturally in a food—as they do in beans and lentils—they can slow down digestion and absorption. The same can happen when protein and fat are included as part of a balanced mixed meal.
This is another reason why what you eat your carbohydrate with matters.
A carbohydrate food eaten on its own may have a different effect from that same carbohydrate eaten as part of a meal containing vegetables, protein and healthy fats, especially if the food is higher GI. That is why we encourage you to eat a bit of low fat yoghurt (which contains protein and fat) with a tropical (higher GI) fruit.
4. The type of sugar
Different sugars are digested at different rates. But remember: sugar isn't automatically "evil." The bigger issue is that sugar is a concentrated source of energy, and many people consume far more of it than they realise—particularly through sweetened drinks and highly processed foods. So, e.g. lactose which is naturally contained in milk and yoghurt is low GI and many fruits are low GI.
The goal isn't to panic every time you eat something sweet. It's to understand the difference between a small amount of sugar as part of an overall balanced diet and a diet where a large proportion of your energy comes from concentrated, refined carbohydrate sources.
So... should you never eat high-GI foods?
No, you should, but only in specific situations - this is where the GI gets really interesting.
There is no such thing as a universally "good" or "bad" carbohydrate.
A food's GI is only part of the story. You also need to consider:
How much you eat
What else you're eating with it
When you're eating it
How active you are
A high-GI carbohydrate can actually be useful in certain situations.
For example, during prolonged endurance exercise, your body needs readily available carbohydrate to maintain energy levels. Higher-GI foods can also be useful immediately after exercise when your muscles are actively replenishing their glycogen stores and absorb most of the higher effect on blood glucose.
So, a sports drink that might not be the best choice for someone sitting at a desk or driving a car all day could be exactly what an endurance athlete needs during and after a marathon. Context matters.
That's why we don't believe in labelling foods as simply "good" or "bad." We believe in understanding what your body needs, when it needs it, and how much.
Glycemic Load: Why portion size matters too
This is where Glycemic Load (GL) comes in...
GI tells you how quickly a carbohydrate is absorbed.
GL takes it one step further by considering how much carbohydrate you're actually eating in a portion, while taking its GI into consideration.
The formula is: GL = carbohydrate in the portion × GI ÷ 100
This is important because a food can have a relatively high GI but still have a low GL if the portion doesn't contain much carbohydrate, like pumpkin.
Take watermelon for example: Watermelon has a relatively high GI of 72, but a normal portion contains a relatively small amount of carbohydrate because it's mostly water.
A 150g portion (about 1 cup of watermelon cubes) contains around 10g of carbohydrate, giving it a GL of approximately 7.
But if you eat four cups of watermelon in one sitting, you're consuming significantly more carbohydrate, and the GL will be much higher.
The same principle applies to dried fruit. An average apple is a low-GI food, and a medium apple has a GL of around 7. But eating an entire 500g packet of dried apples is a very different story. Its GL would be around 50—a huge difference, despite the fact that dried apples are still considered low GI.
The takeaway? Don't look at GI in isolation.
The amount you eat matters - and so does the way you combine foods.
Here's a real-life example:
South African brown bread has a GI of over 70, and the GL of two slices is approximately 30, because two slices contain a substantial amount of carbohydrate.
That means a sandwich made with two slices of brown bread on its own can have a significant effect on blood glucose levels, leaving you hungry in a while.
But imagine you have a thin slice of brown bread as part of a balanced meal containing approximately:
½ cup low-GI baked beans
1–2 slices of ham
Other salad vegetables
a small portion of good fat e.g. avocado
Now the GL of the entire meal is lower and more acceptable—approximately 22 and should sustain you till the next meal, while needing only a fruit in-between.
Notice what happened. Two slices of brown bread on their own have a higher GL than an entire mixed meal containing one thin slice of brown bread combined with low-GI foods, protein, good fat and vegetables.
And you can lower the GL of that meal even further—from around 30 to approximately 20—by choosing two slices of lower-GI bread instead of brown bread.
This is why we don't believe you need to look at individual foods and declare them simply "good" or "bad." So, YES, you can eat bread! But...
The portion size matters.
The quality of the carbohydrate matters.
And what you eat alongside it matters.
A carbohydrate that might have a significant effect on blood glucose when eaten alone can have a much smaller effect when eaten in a sensible portion as part of a balanced meal. That's the power of understanding Glycemic Index and Glycemic Load, as well as the art of combining food.
You don't have to fear, avoid, or cut out carbohydrates! You just need to learn how to eat them smartly.
The best carbohydrate is the one that works with your whole meal
Here's an example. You could eat:
Option 1: A large portion of fatty meat, fish, chicken or cheese with no starch and a large serving of vegetables covered in oil.
Or you could have:
Option 2: A moderate portion of lean meat, fish, or chicken, a small portion of low-GI starch and plenty of vegetables or salad.
The second meal gives you a more balanced combination of carbohydrates, protein, fat and fibre. It's satisfying. It provides sustained energy. It's probably lower in energy (kJ). And it's much easier to eat this way for the rest of your life.
That's the goal. Not to remove carbohydrates from your diet. Not to live on bacon and eggs. Not to spend your life terrified of bread. But to learn which carbohydrates work best for your body—and how to eat them in the right amounts, at the right times, as part of a balanced meal.
Your energy levels are telling you something
Many people don't realise how closely their blood glucose levels can affect the way they feel. When your blood glucose drops too low, you may feel tired, shaky, lethargic or unable to concentrate. When it rises rapidly, you may experience an energy crash later as it falls again...
... That afternoon slump.
... The fuzzy brain.
... The sudden craving for something sweet.
... The feeling of needing a quick energy hit to get through the next few hours.
These can all be signs that your eating pattern isn't giving you the sustained energy you need.
The Smart Health approach is to use lower-GI carbohydrates when you're inactive and even before exercise, while reserving higher-GI carbohydrates for situations where your body can use them most effectively—such as during prolonged endurance exercise and immediately afterwards.
This is the foundation of what we call GI Smart eating.
Don't skip meals to "save calories"
We see this one all the time. Someone decides they're going to be "good" and skips breakfast. Or they have a tiny lunch because they're trying to lose weight.
By late afternoon, they're starving.
By dinner, they're ravenous. And suddenly they're eating everything they can find!
... Then comes the guilt."I'll be better tomorrow." And the cycle starts all over again.
If you've ever found yourself standing in the kitchen at 6pm, eating something straight from the packet because you're absolutely starving, this may be why.
The answer isn't more willpower. It's eating regularly and balanced enough that you don't reach the point of desperate hunger.
A balanced, lower-GI breakfast can help keep your energy levels steady for several hours. A balanced lunch prevents you from arriving at dinner completely depleted. Regular meals, sensible portions and smarter carbohydrate choices work together.
You don't need to white-knuckle your way through hunger. You need a way of eating that keeps you satisfied.
The Smart Health way to eat carbohydrates
For most people, the simplest approach is:
Choose mostly slow-digesting, lower-GI carbohydrates and whole grains.
Eat them in sensible portions.
Pair them with vegetables, protein and healthy fats.
Eat regularly rather than skipping meals and playing catch-up later.
Use higher-GI carbohydrates strategically when your body genuinely needs rapid energy—such as during prolonged endurance exercise and immediately afterwards.
And remember:
GI is a tool—not a set of food rules. You don't need to calculate the GI and GL of every bite of food you eat for the rest of your life.
If you focus on choosing mostly lower-GI, minimally refined carbohydrates, eating plenty of vegetables and whole grains, balancing your meals and controlling your portions, the rest becomes much easier.
You can still eat bread.
You can still eat pasta.
You can still eat rice.
You can even enjoy cake.
The goal isn't to ban carbohydrates. It's to stop treating all carbohydrates as if they're the same.
When you understand how different carbohydrates affect your body, you can make smarter choices that support stable blood sugar, sustained energy, healthy weight and long-term health—without living in fear of food.
That's what being GI Smart is all about.
Want to know which carbohydrate foods are low GI, intermedaite GI and high GI? Buy the Smart Carb and GI Guide from www.gifoundation.com and learn how to swop and use low GI choices rather than higher GI options.
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AUTHOR: ELIZABETH (LIESBET) DELPORT - Registered Dietitian, M.Sc. Dietetics.
Liesbet Delport has over 40 years of experience helping over 10,000 people improve their health through practical, evidence-based nutrition.
After struggling with her own weight as a teenager, Liesbet learned that lasting health isn't about willpower or another restrictive diet. Her approach is simple: people aren't failing, the diets are. She helps people build a balanced, delicious way of eating they can actually follow for life.
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