Among the three types of macronutrients, carbohydrates are probably the most controversial. Some say that carbs are beneficial, while others who’ve cut back on their overall carb intake have achieved lower blood sugar and even weight loss. The reality is that not all carbs are equal — which leads us to the concept of slow-digesting carbs.
For those who are not ready to give up carbs or prefer having them for their workouts and to get more fiber in their diet, choosing slow carbs is the way to go.
This article helps you understand the difference between slow-digesting and fast-digesting carbs, and what to eat for your health and performance.
Slow-digesting carbs, also called slow-releasing carbs or slow-acting carbs, are the type of carbohydrates that are slowly absorbed in the body. They’re low on the glycemic index (GI), meaning that they have minimal effect on your blood sugar (*). Examples of slow carbs include leafy greens, bell peppers, cauliflower, broccoli, carrots, eggplant, and quinoa.
While slow-release carbs release glucose in your bloodstream more slowly, fast-digesting carbs are the opposite. These carbs are high on the glycemic index, causing your blood sugar to spike. Given that fast-digesting carbs serve as a quick source of energy, they’re best consumed before or after workouts, especially workouts that involve quick bursts of energy — e.g. sprinting, jumping, and heavy lifting.
Examples of fast-digesting carbs include white rice, white bread, pasta, bananas, pastries, regular soda, fruit juices, and highly processed foods with added sugars. Consuming large amounts of fast-digesting carbs more frequently may lead to increased cravings and overeating (*). According to research, high GI diets are linked to type 2 diabetes, increased heart disease risk, and certain cancers (*).
Foods that digest slowly possess certain qualities. If you’re looking to eat more slow-release carbs for their health benefits, choose those that are high in fiber, have a low GI rating, and are unprocessed. Let’s dive into each quality in the next paragraphs.
Fiber is a type of carbohydrate, although the body is unable to digest it. If you’re at risk of diabetes or already have the condition, fiber reduces the rate at which glucose is absorbed (*). Besides slowing glucose absorption, fiber increases your perceived satiety, helping control your appetite (*). It may not be necessary to completely forgo carbs if you can opt for high-fiber foods instead.
A low GI score of 1 to 55 is another important characteristic of slow-digesting carbs. For example, broccoli (a slow carb) has a GI value of 15 while white bread (a fast-acting carb) has a GI value of 100. Between the two, white bread should be avoided if you’re trying to lose weight or maintain healthy blood sugar levels — unless you need quick energy close to your workout.
Many foods in their whole unprocessed forms, such as vegetables and fruits, are sources of slow-acting carbs. When buying fresh produce, opt for the ones that are high in fiber and low on the glycemic index. In contrast, many processed foods, such as potato chips and biscuits, are classified as fast-acting carbs.
Essentially, slow-digesting carbs are better than fast-acting carbs in many aspects. Obtaining most or all of your carbohydrate needs from these foods can speed up weight loss naturally, boost cognition, and reduce your risk of metabolic disease.
Here’s how slow carbs can be good for you:
Steady release of energy
As mentioned previously in this article, fiber (whether soluble or insoluble) take longer to digest. For this reason, blood sugar rises more gradually, allowing you to experience stable energy for hours — without the highs and lows.
On the contrary, foods with a high glycemic load are more likely to cause fatigue and even mood disturbances (*).
May improve blood sugar control
The fiber that’s present in slow carbs takes longer to digest, lessening a food’s impact on your blood sugar. This makes slow-digesting carbs a healthier option for individuals who have diabetes. Large prospective studies have consistently shown that a higher fiber intake is associated with a 20–30% lower risk of type 2 diabetes (*).
May enhance satiety and supports weight management
Satiety is one of the keys to losing weight and keeping it off. Instead of cutting calories, filling up on foods that make you satisfied but do not spike your blood sugar is a winning option to become fitter.
Most studies find a trend between low glycemic index diets and weight loss (*). Additionally, studies done on animal models show that high GI starches favor weight gain and visceral adiposity (the fat stored deep inside your belly and wrapped around your organs) (*).
May improve cognitive function
Fast-acting carbs, which are a source of simple carbs, have been consistently associated with decreased global cognition. Conversely, complex carbs, which release glucose gradually, correlate with healthy brain aging and improved short-term and long-term memory (*).
May promote cardiovascular health
A diet that is high in fast-acting, high-glycemic carbs may increase serum triglycerides (*). Triglycerides are a type of fat that supply energy to your body.
While they’re important, having too many triglycerides increases your likelihood to develop atherosclerosis or plaque buildup in your arteries (*). Blockages in your arteries may eventually lead to complications, such as stroke, heart attack, and erectile dysfunction (*).
Slow carbs, such as leafy greens, broccoli, cucumbers, nuts, and avocados may help increase HDL levels (high-density lipoprotein, your good cholesterol). HDL plays a vital role in mobilizing cholesterol and protecting against heart disease (*).
Slow-release carbs include fruits and vegetables containing good amounts of fiber and are low in sugar. Dairy products, as long as they’re unflavored, can also be part of a diet focusing on slow digestible carbs. Check out the list below:
- Bell peppers
- Salad greens
- Green beans
- Nuts (almonds, pecans, walnuts, etc.)
- Seeds (chia, sunflower, pumpkin, etc.)
- Cheese (cheddar, parmesan, mozzarella, etc.)
- Plain, unflavored yogurt
Since slow-digesting carbs or complex carbs pack more nutrients and lead to longer-lasting energy, the best times to take them are during breakfast, 2-3 hours before your workout, at snack time (if you need extra energy in the afternoon), and in the evening (for those who have difficulty falling asleep).
Some people would rather have black coffee for breakfast instead of a meal, but for those who eat breakfast, slow carbs are a healthy choice. Pair them with protein and fats. For example, spinach with eggs and cheese omelet!
If you’re planning to have your workout in a few hours, it’s better to get fuel from complex carbs. You can have a bowl of quinoa with chicken and broccoli. This pre-workout meal consists not just of slow carbs, but also essential amino acids, vitamins, and minerals. (Note: Fast-acting carbs are best consumed closer to your workout, at around 30-60 minutes, since they break down more quickly.)
For people who are active, eating a snack may help beat hunger and the afternoon energy slump. Combine almonds and slices of cheese to increase your energy without experiencing a crash. Remember to avoid anything with sugar.
Carbohydrates can help with sleep by facilitating the uptake of tryptophan — an amino acid that gets converted to melatonin, which promotes sleep — by the brain (*). If you have trouble winding down or you experience low blood sugar at night, have a small snack with slow carbs, such as a handful of nuts, Greek yogurt with berries, or baby carrots and cucumber slices.
On top of prioritizing slow carbs, it’s important to determine how many carbs you need in a day. For people on a very low-carb keto diet, this means consuming less than 50 grams of complex carbs daily. However, if you’re someone on a standard low-carb diet, you can eat up to 150 grams of complex carbs. Tracking your carbs can be very useful if you’re struggling to lose weight and keep your blood glucose at a healthy range.
Another beneficial tip is to rotate your food sources. Since foods vary in their nutrient content, it helps to eat a wide range of slow carbs. For example, broccoli and leafy greens this week, and asparagus and green beans for the next week — you get the idea. Do this along with varying your protein and fat sources as well.
Based on what you’ve learned so far, carbs can be part of a diet plan that supports weight loss, healthy blood sugar levels, and other benefits. The key is to be mindful of quality, which makes slow carbs a better option.
Note that focusing on slow carbs doesn’t mean reducing your overall carb intake, although it tends to be the case with people who follow a keto diet. Remember to eat a variety of slow-release carbs to get as many nutrients as possible.
Siti N et al. Unravelling the Effects of Soluble Dietary Fibre Supplementation on Energy Intake and Perceived Satiety in Healthy Adults: Evidence from Systematic Review and Meta-Analysis of Randomised-Controlled Trials. 2019 January