The nutrition impact of carbohydrate

High-carb diets were almost universally embraced for several decades, but the growing popularity of low-carb diets has tarnished public perception of high carbohydrate intakes a little bit. Just as fat’s historically bad reputation was overblown and generally undeserved, the more recent backlash against carbs is similarly overblown and largely lacks justification.

Carbohydrates are not “nutritionally essential.” While sufficient dietary intake of essential fatty acids and essential amino acids are required for survival, the same cannot be said for carbohydrates. Nonetheless, carbohydrates play an important role in providing energy for high-intensity exercise (including both cardio and resistance training), and there are numerous health benefits associated with a wide variety of high-carbohydrate foods. For example, high-carb foods often provide plenty of fiber that is good for supporting satiety, blood glucose regulation, and gastrointestinal health. Fruits and vegetables are also made up of mostly carbohydrate (rather than fat or protein), and both provide a wide range of vitamins, minerals, and other biologically active phytonutrients. In summary, you could technically survive without carbohydrate, but carbs play many important roles in the typical diet (and an even more important role in the diet of athletes who train or compete in high-intensity activities).

Carbohydrates can be divided into a number of distinct subtypes. Perhaps the most simplistic method of categorization is to classify carbohydrates as either “simple” or “complex.” Simple carbs refer to sugars, whereas complex carbs refer to starches and dietary fibers. There are a handful of different types of sugars, but the most commonly discussed sugars tend to be glucose, fructose, and sucrose. Sucrose is table sugar, and it’s made of a 50:50 split of glucose and fructose. Glucose is a particularly noteworthy component of table sugar; it’s a key energy source for our brains, it provides the building blocks for starch and glycogen, and our ability to regulate its concentration in our bloodstream is a critical indicator of health. Fructose is commonly found in fruit (alongside some glucose and sucrose), but it is also consumed in the form of high-fructose corn syrup. It’s commonly believed that fructose has a deleterious impact on cardiometabolic health, even at fairly modest intake levels, which has led to widespread concerns about the health effects of high-fructose corn syrup.

Much like regular table sugar, high-fructose corn syrup is just a mixture of glucose and fructose. Few people are intentionally seeking out high-fructose corn syrup in their diet, but it just tends to show up in products that use it as a sweetener. While sucrose (table sugar) is a 50:50 mixture of glucose and fructose molecules that are chemically bound together, the exact mixture of high-fructose corn syrup can be customized, and the glucose and fructose molecules are not bound together. That missing chemical bond is effectively irrelevant, but some high-fructose corn syrup mixtures have higher fructose concentrations than table sugar. A very common version found in many soft drinks contains 55% fructose and 45% glucose, but that isn’t the only variety. For example, many food products (including cereal, baked goods, and other processed foods) use corn syrup with 42% fructose (lower than table sugar), while some candies and other super-sweet products use fructose ratios much higher than 55%.

Sucrose contains glucose (left side) bound to fructose (right side). During digestion, the bond in the red circle is promptly broken. In high fructose corn syrup, the bond is not present

There certainly aren’t any notable health benefits associated with high-fructose corn syrup, but a lot of the negative stuff you’ve heard about it is probably exaggerated. Glucose and fructose are simply metabolized a little bit differently in the body, and very high fructose intakes can have unfavorable effects on your liver and blood lipids. It’s pretty tough to unintentionally get troubling amounts of fructose from eating whole fruits, but you can achieve some remarkably high intakes of fructose if you’re consuming a lot of processed, hyper-palatable, high-calorie foods and beverages like soda, juice, and candy. So, there is a biochemical basis for some of the concerns related to fructose, but you don’t have much to worry about if you’re physically active, eating an appropriate amount of total energy, and eating a fairly balanced diet. In healthy, active, weight-stable people, even extremely high fructose intakes are pretty benign.

So, there’s nothing to fear about carbohydrates, and there are numerous reasons to include them in your diet. As mentioned previously, many carb sources are high in fiber, which is great for regulating hunger, glycemic control, and bowel movements, while also being inversely associated with a number of cancers and chronic diseases. High-fiber carb sources, such as certain fruits, vegetables, and whole grains, also provide a wide range of vitamins, minerals, and phytonutrients that are important for optimal health and function.

Finally, sufficient carbohydrate intake can support performance and body composition goals. When we consume carbohydrates, some of the carbs are immediately used for energy, and a large portion is stored as glycogen (primarily in our muscles and liver) for later use. High-intensity exercise requires plenty of carbohydrate availability to produce energy rapidly enough to sustain performance, so we want to have plenty of glycogen stored up prior to an exercise bout. Insufficient carbohydrate availability can impair sprint performance, muscle contractile function, and strength performance, and muscle and liver glycogen levels get depleted during exercise. So, adequate dietary carbohydrate provides us with plenty of fiber, micronutrients, and substrate to fuel high-intensity exercise.

Incorporating Carbohydrate Into a Diet

When we’re sitting around and resting, our body is mostly utilizing fat for energy. As we start performing light exercise, we progress to using a slightly larger proportion of carbohydrate for energy needs (if it’s available), and a slightly lower proportion of fat. This carbohydrate will either come from a pre-exercise carbohydrate-rich meal, or from glycogen that was stored after we consumed carbs in previous meals. Relative carbohydrate utilization increasingly ramps up as exercise intensity increases, so high-intensity strength and sprint work is heavily reliant upon carbohydrate for energy. For this reason, the optimal amount of carbohydrate in the diet can be heavily influenced by the amount and intensity of exercise someone performs.

Graphical representation of relationship between exercise intensity and substrate utilization with arbitrary values

If you do a ton of endurance exercise, you’ll need more carbs than a sedentary person. Even if your intensity remains pretty moderate and carbs make up only a small relative contribution to your energy needs during exercise, the sheer amount of total exercise volume will ensure that you’re burning through plenty of carbs that will need to be replaced. Of course, the same is true if you complete an appreciable amount of high-intensity exercise; even though the total volume of exercise isn’t likely to be extremely high, the intensity of the effort will ensure that even modest amounts of training volume will lead to substantial carbohydrate utilization. If the volume or intensity of your exercise results in heavy carbohydrate utilization and you fail to replace it via dietary intake, the result is pretty simple: performance suffers in subsequent bouts of exercise.

So, if you’re primarily focused on performance and your training (or competition) involves physical tasks with intensities higher than a slow trot and volumes higher than a set of a few resistance training repetitions, you’ll want to make sure you have sufficient carbohydrate available to fuel your efforts. Determining how much is enough will ultimately depend on the specific physical demands of your exercise; as volume and intensity increase, the relative demand for carbohydrate increases as well. So, the typical lifter on a low-volume resistance training program with low rep ranges doesn’t exactly need to force-feed carbohydrates, but an avid endurance athlete in a tough phase of training definitely ought to prioritize carbs in their diet. For avid endurance athletes, it’s probably not a bad idea to aim for at least 6g of carbs per kg of body weight, whereas the typical lifter can probably get by with at least 3-4g/kg.

If you don’t exercise, your workouts are minimally carb-dependent, or performance during your workout sessions isn’t critical to you, then you have a lot more wiggle room when balancing the calories from carbohydrate and fat in your diet. Nonetheless, independently of exercise considerations, there are still some good reasons to consume a fairly balanced diet with moderate intakes of carbohydrate and fat. For non-exercisers who are just aiming for balanced macronutrient intakes, a carb intake of around 40-60% of total calories is pretty typical, which should facilitate a diet rich in fiber, micronutrients, and phytonutrients, as long as carbs are obtained from a diverse selection of nutrient-dense foods.

Without question, some people prefer low-carb diets for a variety of reasons. For example, some people simply find that low-carb diets fit their food preferences better than low-fat diets do, and others find low-carb diets to be more satiating per calorie. Low-carb diets are not significantly more effective for losing fat, building muscle, or improving cardiometabolic health than low-fat diets with similar protein and calorie content, but they are a viable dietary option nonetheless. A typically low-carb dieter will often set carbs at 30% of energy or lower (up to an absolute upper limit of about 200g/day). For a more extreme approach, ketogenic diets involve even more intensive carbohydrate restriction, with daily intakes rarely exceeding 50-60g or so. Again, ketogenic diets are not inherently better than low-fat diets, and probably aren’t ideal for hypertrophy or bulking, but they are an option for individuals aiming to lose or maintain weight.

So, if performance during high-intensity exercise (or moderate-intensity exercise for extended durations) isn’t a top priority, you have a ton of flexibility for setting your dietary intake. One could choose to adopt a ketogenic or low-carbohydrate approach, although higher carb intake is typically the “default” approach, with 40-60% of energy coming from carbohydrates. For individuals with a large emphasis on exercise performance, dietary carbohydrate needs scale upward with the carbohydrate demands of their exercise. To avoid performance decrements related to low carbohydrate availability, the typical lifter should consider aiming for at least 3-4g/kg of carbs per day, while those regularly engaging in endurance exercise should consider aiming for at least 6g of carbs per kg of body weight. This is assuming, of course, that you’ve got enough calories to make that work after meeting your needs for dietary protein and fat (which might not always be the case).

MacroFactor is totally compatible with a wide range of dietary preferences, and gives you the option to select guidance for low-carb and ketogenic approaches. No matter which dietary setting you choose, relative intakes of fat and carbohydrate will be recommended based on your body composition, goals, exercise habits, dietary preferences, and recommended total energy intake, with care taken to ensure that you have adequate amounts of protein and fat in your diet.

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