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In some quarters, carbs get an undeserved bad rap. But students of human evolution know that dietary carbohydrates (fruits, berries and tubers) played an instrumental role throughout our long 3-million-year journey from a small upright walking ape (Lucy, Australopithicus afarensis) to the tall, smooth-skinned creature with a very large brain who can perform high level maths as well as prolonged strenuous marathons (Homo sapiens sapiens). You could say we evolved eating the original plant-based diet. The challenge today however, is to ensure we consume the high-quality carbs similar to the ones our ancestors ate that are digested at a rate that our bodies can accommodate, preventing burnout of our insulin-producing machinery. In Food for Thought, we answer some of the questions we are asked about the high-quality carbs we like to call “good carbs”. 

Good carbs
WHAT DO CARBS DO? Our brains, nervous system, red blood cells, kidneys and muscles during exercise prefer carbs as their energy source. Carbs also give our cells structure, form part of our genes and play a part in the function of some proteins. Did you know that glucose powers the growth of a healthy human fetus born with substantially more body fat than any other primate.

WHAT ARE CARBS? Carbohydrates are made up of carbon, hydrogen and oxygen, so you can see where the name comes from. You may recall seeing it written up in your high school science books as CHO. For example, the chemical formula for glucose is C6H12O6 which stands for six carbon atoms and six water molecules (H2O = one water molecule; six water molecules = H2O x 6).

All plant foods contain carbs to a greater or lesser extent—fruits, vegetables, legumes, grains and nuts—as do milk and yoghurt, but not most cheeses (the whey is drained away so it is just protein and fat).

WHAT ARE GOOD CARBS? These are the plant foods the natural world has provided for us: fruits and berries, vegetables, beans, peas, lentils, seeds, nuts, and grains and the traditional staple foods and dishes we make from them such as noodles, pasta and grainy, seedy breads.

WHAT ABOUT MILK? Dairy foods such as regular milk and yoghurt are good carbs too. And let’s not forget mother’s milk which provides the perfect mix of carbs, fat, protein, vitamins and minerals for our babies to grow and thrive for the first six months of life. Mother Nature made it sweet so it is very appealing to babies. The sweetness comes from a special sugar called lactose only found in milk. Human milk has one of the highest concentrations of lactose of any mammal coming in at around 7 grams of lactose per 100 millilitres (3½ fluid ounces) which in household measures is little over ⅓ cup. It contains almost 50% more than that of cow’s milk. Why so much? One reason is probably to satisfy our fast-growing, energy-hungry, glucose-demanding brain. Scans show that a baby’s brain reaches more than half adult size in the first 90 days of baby’s life. Mother’s milk also contains special carbs called oligosaccharides (think of them as prebiotics), which friendly bacteria in the large intestine chomp on to thrive.

WHAT’S SO GOOD ABOUT GOOD CARBS? They are sustaining and sustainable foods that come with a swag of micronutrients we need for good health including vitamins B, C and E; minerals such as magnesium, potassium and calcium and antioxidants including the carotenoids that play a protective role in eye health. Dan Buettner’s Blue Zones studies provide compelling evidence that dietary patterns that are rich in good carbs and dietary fibre reduce the risk of weight gain, type 2 diabetes, coronary heart disease and certain kinds of cancer, like colorectal cancer.

HOW MUCH CARBOHYDRATE DO WE NEED? Our diet is not limited to One Size Fits All. You only have to look around the world to see that there are very different dietary patterns with very different fuel mixes associated with good health and long life. Traditional Mediterranean and Japanese diets which are both linked with a long and healthy life couldn’t be more different. The Mediterranean diet is relatively high in fats and tends to be rather moderate in carbs. The Japanese diet, like most Asian diets, is high in carbs and low in fats. What they have in common and what seems to matter most is that they are based on good, wholesome foods and ingredients. Mostly plants.

WHAT ABOUT BLOOD GLUCOSE? When we eat carb-rich foods, our bodies convert their sugars and/or starches into glucose during digestion. However, our bodies do this at very different rates and this is where using the glycemic index (GI) helps us make better choices for long-term health and wellbeing. The GI is particularly useful for people who need to manage their blood glucose levels (BGLs). Think of it as a carbo speedo that gives us an idea how quickly our bodies will digest particular carb foods and how fast and high our BGL is then likely to rise.

Research around the world over the past forty years shows that switching to eating mainly low GI carbs throughout the day that will trickle glucose into our bloodstream and lower our day-long blood glucose and insulin levels helping us:

  • Manage our appetite because we will feel fuller for longer 
  • Minimise our body fat 
  • Maximise our muscle mass 
  • Decrease our risk of type 2 diabetes and heart disease. 

IS RESISTANT STARCH A GOOD CARB? It is starch that resists digestion and absorption in the small intestine and zips through to the large intestine largely intact to be fermented into short chain fatty acids, like acetate, propionate and butyrate by those good gut bacteria we have down there. Research in recent years suggests it may well be as important as fibre in helping reduce the risk of colorectal cancer, so it has a lot of fans. It’s found naturally in unprocessed cereals and whole grains, firm (unripe) bananas, beans and lentils. But you can create it in your own kitchen too when you make potato salad, rice salad or pasta salad—starchy foods that you cook and then cool. The same goes for old-fashioned oatmeal if you cook up a pot one day and reheat individual portions the next.

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