A low-carb diet is a buzz word most of us are familiar with. It has gained popularity with scientific evidence supporting its benefits in losing weight and controlling blood sugar, among other benefits.
A low-carb diet generally means that you eat fewer carbohydrates and a higher proportion of fat and an adequate amount of protein — low-carb-high-fat diet or ketogenic (keto) diet.
When someone questions my love for eating vegetables like broccoli and asparagus for example, while on a ketogenic-diet, it makes me a little uneasy. Not because of their lack of awareness, but because of the feeling that as scientists we have failed to deliver that knowledge to the general public (the real end-users of our research outcomes).
So let me take the opportunity to make things clear …
For those who think a low-carbohydrate diet is the same as a low-fibre diet, and have been staying away from all types of plant foods, you, my friend, are mistaken — either misinformed or only half-informed.
Carbohydrates and dietary fibre are no doubt interlinked but are distinctly different when it comes to their activity in our body.
Now, for people who might think that this is another article in support of a plant-based diet and/or to demonise the carnivore diet, here is a disclaimer — I have been following a keto diet (not a strict one) and intermittent fasting for the last 4 years and am a meat-eater who loves veggies/fruits/nuts equally.
Now, that I have cleared my stance on feeding my body without any bias towards any particular food group, let’s get back to the science.
Carbohydrate and dietary fibre — two brothers (or sisters) from the same mother
Carbohydrates, proteins and fats are the three main sources that deliver energy (or calories) for our bodies to function.
You might remember from your chemistry class that carbohydrates are made up of carbon, hydrogen and oxygen. Carbohydrates are found in fruits, grains, vegetables and milk products.
Most foods contain carbohydrates, which our body breaks down into simple sugars (like glucose or fructose) by using the enzymes in our saliva, stomach and small intestine.
As this sugar enters the blood, the blood sugar levels rise and the pancreas produces insulin, a hormone that signals our cells to absorb sugar for energy or storage. Increasing blood sugar levels leads to a spike in insulin secretion by the pancreas.
Extra glucose is stored in our muscles and liver as glycogen, that can be broken down into glucose if your body needs quick energy. If glycogen stores are filled, glucose is then stored as fat.
If this cycle continues, you are at increased risk of developing insulin resistance, a hallmark of Type 2 Diabetes, Metabolic Syndrome, heart diseases, and many others.
But not all carbohydrates get digested to be absorbed and affect blood glucose levels. The fibre component of the carbohydrate for instance, gets fermented into important metabolites that can confer health benefits including immunity.
The key is to choose your carbohydrates cautiously
Carbohydrates can be categorised into three groups:
- Simple carbs (Sugars)
- Complex carbs (Starches)
- Indigestible carbs (fibre)
The difference between these groups is the chemical structure and how quickly the sugar is absorbed and digested (or not digested as in the case of fibre).
1. Simple carbohydrates :
Simple carbs are made up of simple sugars.
Some are made up of a single sugar molecule (monosaccharides) — glucose, fructose and galactose (a milk sugar).
While others are made up of two sugar molecules joined together (disaccharides)— the best known example is sucrose or white sugar that is made up of fructose and glucose. Other examples include lactose (a milk sugar made from glucose and galactose) and maltose (a sugar found in cereals, made from two glucose molecules joined together).
Monosaccharides and disaccharides are rapidly absorbed from our intestine into circulation (due to their relatively simple chemical structure), most rapid being the glucose. This results in a rapid rise in blood sugar levels and insulin secretion from the pancreas — this can have negative health effects, especially if you consume foods containing high levels of white refined sugars (unfortunately, that is pretty much everything these days).
Note: Nutritious foods like fruits and milk also contains these simple sugars. But they also provide other important nutrients like vitamins, antioxidants, fiber, and calcium.
2. Complex carbohydrates :
As the name suggests, complex carbohydrates have complex chemical structures — like the starch.
In starch, sugar molecules are chained together to form complex carbohydrates (polysaccharides) — found in rice, wheat flour and potatoes.
Foods with complex starch also influence blood sugar levels but at a sustained rate compared to simple sugars. The glycaemic index is a more effective measure of predicting the effect of complex carbohydrates in starchy foods on blood sugar levels and their role in chronic diseases.
The glycaemic index ranks carbohydrates on a scale from 0 to 100 based on how quickly and how much they raise blood sugar levels after eating.
- Foods with a high GI (70 and above) have a rapid affect on your blood glucose levels — eg. white bread, boiled white rice, cornflakes, potato chips. These foods are rapidly digested, spiking the blood glucose and giving us a short-burst of energy that then fades off, making us hungry again after a short period of time.
- Foods with a medium GI (56–69) produce a more sustained effect on blood glucose levels — eg. boiled brown rice, banana, sweet potato. They take longer to digest and absorb, allowing for a more sustained energy over a longer period of time.
- Foods with a low GI (less than 55) contain fewer carbohydrates, or carbohydrates that break down slowly to produce only a small effect on blood glucose levels — eg. wholemeal bread, chickpeas, kiwifruits. These foods tend to release glucose slowly and steadily and are best to counter weight gain.
Choose your complex carbs wisely
Carbohydrates are often accused of contributing to weight gain, but if you choose the right kinds of carbohydrates, they can actually help you achieve your health goals — prevent weight gain, lose weight or maintain blood glucose levels.
Foods with a high-GI index are most often processed and ultra-refined, stripped of other nutrients. They are cheap, easily accessible and ready-to-eat, making them an attractive option.
Ultra-refined, ready-to-go meals are like those low-quality batteries that boost the performance of your device before running out of juice only after a few months or even sometimes weeks. They cost relatively little compared to some higher quality batteries that offer sustained performance for years. For the long-term, high-performing batteries that provide sustained power to your device is a much wiser investment.
Ultra-refined foods are worst in terms of providing us energy, as they are short-lived, leaving us feeling hungry after an initial spike in energy levels. Plus, they contribute to the development of chronic metabolic diseases due to their impact on blood glucose levels. So do not fall for their low-cost tactics.
The slow and steady release of glucose in low-glycaemic foods helps maintain good glucose control. Some of these foods, like vegetables and whole-grains, however, are costlier and require preparation, cooking and some of the effort required to make a trip to a supermarket. But the benefits associated with them outweigh the costs and effort, especially if good health is your priority.
Choose your food wisely for its carbohydrate content and GI index to help you make better food choices to keep you fuller for longer and that have minimal effect on blood glucose levels.
You can find out the glycaemic index of some of the common foods using this link http://www.glycemicindex.com/ .
A number of factors are known to affect the GI index of foods.
- Processing — Grains that have been milled and refined tend to have a higher GI than minimally processed whole grains.
- Physical form — Finely ground grain is more quickly digested than coarsely ground grain. Oats for instance, are therefore more healthier than a highly processed whole-grain bread.
- Ripeness — Ripe fruits and vegetables are more likely to have a higher GI than un-ripened fruits.
- Fat content and acid content — Meals with fat or acid are converted more slowly into sugar, thus tending to have less impact on blood glucose levels.
- Fibre content — High-fiber foods contain less digestible carbohydrates, which slows the rate of digestion and causes a more steady and lower rise in blood sugar.
3. Indigestible carbohydrates :
Fibre is an indigestible carbohydrate. This means fibres cannot be broken down into sugars during digestion in our small intestine unlike the simple and complex carbs (in fact, it slows digestion and absorption of carbohydrates).
Fibres are passed into our large intestine (also known as colon) where they help feed the microbiota in our gut (fermentation), which breaks down fibre to products that help support a healthy digestive system and protect against gut and other diseases.
Fibres are of two types — soluble and insoluble. Many fiber-rich foods contain some of both and hence, both are beneficial to health. Resistant starch, while not exactly a type of fibre, acts in a similar way to fibre. Because they all have different health benefits, it’s important to include all the three in your diet.
Soluble fibres: can dissolve in water. They are found in a variety of foods including oats, legumes, fruit, vegetables and seeds. It can provide numerous benefits: — help you feel full, reduce the amount of cholesterol absorbed from the small intestine and also help stabilise blood glucose levels.
Soluble fibre dissolves in water and gastrointestinal fluids in our body and forms a gel-like structure that slows digestion, and upon reaching the large intestine, gets fermented by the microbiota.
Insoluble fibres: does not dissolve in water. It attracts water into your stool, adds bulk to the stool, and makes it easier to pass with less strain on your bowel. Insoluble fibres can prevent constipation by helping food move through your system.
Resistant starch: is a starch that does not get digested in the small intestine. Just like fibres, it gets passed into our large intestine where it feeds the gut microbiota, thus providing health benefits.
All starchy foods contain resistant starch — it occurs naturally in cereals (bread and pasta), legumes (lentils, chickpeas, red kidney beans and baked beans), nuts and some seeds, starchy vegetables, and under-ripe bananas.
The amount of resistant starch varies greatly depending on how food is manufactured, prepared and cooked — as well as if it’s reheated.
Different ways of cooking can produce different amounts of resistant starch. For example, resistant starch is found in slightly undercooked (‘al dente’) pasta and cooled cooked potatoes and rice.
Fibre feeds the gut microbiota
The indigestible fibre is the key to unlocking the health and immune benefits that your gut microbiota can confer. The microbiota feeds on the fibre to produce numerous metabolites with incredible health functions — including short-chain fatty acids, anti-microbials and nuerotransmitters. These metabolites then not only nourish the gut but also provide benefits to distant organs, including our heart, lungs, liver and brain.
It is extremely important to eat a variety of fibres from various fibre-rich foods. This will ensure you are feeding a number of different members of the microbiota and boost your microbial diversity to harness a range of health benefits.
Implications for keto-diet
Yes, you can eat low-carb-fibre-rich foods while on a keto-diet. This actually helps you to sustain the diet for long-term benefit.
I highly recommend this article by Dr. Stephanie Estima that highlights the importance of feeding your gut microbiome while on the keto-diet.
Just because dietary fibre is closely associated with carbohydrates, does not mean it is bad. Do not avoid it. Dietary fibre is like that chap who sometimes earns a bad reputation simply because he hangs around with a bunch of potheads. But in reality, he might not be a stoner. Give him a chance, he could actually make a damn good vocalist for your band, ahem or for orchestrating your microbiota!
Take care of your gut and good health will follow!