Table of contents
- Introduction
- Why are carbohydrates not an essential nutrient?
- What defines a low-carbohydrate diet?
- Are carbohydrates sources for vitamins and minerals?
- Can carbohydrate-rich foods be sources for protein?
- What are good carbohydrates sources of dietary fiber?
- Why would people choose a lower-carbohydrate diet?
- How do carbohydrates affect performance?
- Does a low-carbohydrate diet affect muscle growth?
- Is it sustainable to aggressively restrict carbohydrates long-term?
- Conclusion
Introduction
Carbohydrates and carbohydrate-rich foods play an important role in a balanced diet. This article discusses why carbohydrates matter, not just for energy but also for their contributions to micronutrient and fiber intake. We also highlight how different styles of training and exercise might influence our carbohydrate needs.
Let’s take a deeper look!
Why are carbohydrates not an essential nutrient?
You may have heard that carbohydrates aren’t considered an “essential nutrient,” but that certainly doesn’t mean that carbohydrates are unimportant. Essential nutrients are those that our bodies can’t make on their own, so we need to get them from our diet. For example, when it comes to protein, there are nine essential amino acids out of the twenty that our bodies use. In the case of fats, most of the fats we eat are considered nonessential, but we do need to consume essential fatty acids, which are part of the Omega-3 and Omega-6 families. However, that certainly doesn’t mean that you could build a healthy, balanced diet from nothing but essential amino acids and essential fatty acid supplements. Unlike proteins and fats, there are no carbohydrates that are considered nutritionally essential, but just like proteins and fats, all of those “nonessential” carbohydrates can still be part of a healthy diet.
Carbohydrates contain sugars and starches that break down into glucose in the body. Glucose is an energy source either stored for future use or metabolized through glycolysis, eventually producing ATP, which cells rely on for energy. Our bodies can synthesize glucose through a process called gluconeogenesis, producing glucose from non-carbohydrate sources such as fat and protein. The ability to produce glucose from other nutrients is why carbohydrates are not considered an essential nutrient.
Many argue that since the body can produce glucose endogenously, supplying it from external sources is unnecessary. While it is beneficial that the body can generate glucose and support necessary metabolic reactions without dietary carbohydrate intake, it doesn’t mean it’s ideal to rely on gluconeogenesis for all of the body’s glucose needs.
What defines a low-carbohydrate diet?
There are varied opinions on what defines low carbohydrate intake in lay literature and academia. A scoping review of clinical studies defines low- and very-low-carbohydrate diets as:
Low-carbohydrate diet (LCD)
- Generally defined as ≤30% of daily energy intake from carbohydrates.
- Typically, it ranges from 60 to 130 grams of carbohydrates per day. This aligns with the threshold below which a diet might be considered low-carb by several nutrition authorities.
Very-low-carbohydrate diet (VLCD)
- Defined as <10% of daily energy intake from carbohydrates.
- Typically ranges from 20 to 50 grams of carbohydrates per day and is often aligned with ketogenic diet parameters.
I should state that adequate carbohydrate intake is possible on a low-carbohydrate diet, especially with attentive and diverse meal planning. For instance, if the total daily energy budget is 2000 calories and we utilize 30% for our daily carbohydrate intake, it allows for roughly 150g of carbohydrates. For sedentary people in the general population, or for people engaging in relatively low-volume anaerobic exercise, this carbohydrate budget is still plenty to allow people to meet fiber and micronutrient intake recommendations.
However, a very-low-carb diet can lead to fiber and nutrient issues without careful planning.There can also be issues with optimal performance or muscle growth, which I’ll discuss in a moment.
For more on the carbohydrate needs of different populations, this article has you covered.
Are carbohydrates sources for vitamins and minerals?
While carbohydrates are often discussed for their energy and performance enhancement, many carbohydrate-rich foods also make good sources for vitamins and minerals – most notably, fruits and vegetables. In this recent article on protein quality, I discussed the importance of amino acid profiles. One issue with strict plant-based diets is that some plant-based protein sources lack certain essential amino acids. A similar issue can arise when looking at micronutrient sources. For instance, specific vitamins or minerals might technically be present in protein- and fat-rich foods, but achieving adequate levels from these sources could require consuming much higher calories or eating uncommon foods.
It’s important to note that a high-carbohydrate or high-calorie diet doesn’t necessarily provide optimal levels of vitamins and minerals. There are nutrient-rich and nutrient-sparse carbohydrate-rich foods. This is the major PR problem for carbs: your diet can be rich in fruits and vegetables that provide plenty of fiber and micronutrients, or it can be dominated by simple sugars, yet both might be described as high-carb diets.
That said, carbohydrate-rich foods are not just beneficial; they are also the dominant sources for many micronutrients. For example, while vitamin C can be found in some animal products, it’s usually not found in high amounts of commonly consumed foods. The most common sources of vitamin C are in fruits and vegetables; if you want to get vitamin C from animal sources, you’ll need to make a point of eating liver or lung, not hamburgers or chicken breasts. Though scurvy is rare today, it historically affects those without access to sources of vitamin C (and, even if you’re not at risk for scurvy, low vitamin C intake may still make you more susceptible to infections and decrease your rates of connective tissue synthesis and repair).
Foods high in Vitamin C (per 100 calories)
| Food item | Serving size (grams) per 100 calories | Vitamin C (mg) per 100 calories |
|---|---|---|
| Red bell pepper | 205 | 380 |
| Kale | 297 | 177 |
| Kiwi | 177 | 93 |
| Strawberries | 286 | 90 |
| Broccoli | 294 | 81 |
| Orange | 237 | 59 |
Animal foods high in Vitamin C (per 100 calories)
| Food Item | Serving size (grams) per 100 calories | Vitamin C (mg) per 100 calories |
|---|---|---|
| Pork liver | 125 | 23 |
| Lamb liver | 117 | 13 |
| Cod roe | 114 | 3 |
Source: USDA FoodData Central
Note: These values vary based on the measurement and source of the item.
Folate is another micronutrient that’s virtually absent in most animal products, but is abundant in carbohydrate-rich foods. Vegetables are usually the most convenient and best sources of folate; furthermore, most grain products are fortified with folate in many developed countries.
Folate in plant sources (per 100 calories)
| Food item | Serving size (grams) per 100 calories | Folate (mcg) per 100 calories |
|---|---|---|
| Spinach | 174 | 194 |
| Asparagus | 134 | 164 |
| Brussels sprouts | 88 | 124 |
| Lentils | 77 | 120 |
Folate in Fat and Protein Sources (Per 100 Calories)
| Food item | Serving size (grams) per 100 calories | Folate (mcg) per 100 calories |
|---|---|---|
| Beef liver | 74 | 215 |
| Sunflower seeds | 14 | 80 |
| Flaxseeds | 20 | 72 |
| Eggs | 150 | 47 |
| Chicken breast | 79 | 5 |
Source: USDA FoodData Central
Note: These values vary based on the measurement and source of the item.
While deficiencies exist in all kinds of diets, they present more of a challenge when one macronutrient source is removed or severely diminished. If concerned about micronutrient sources, extra attention should be paid if you’re following a diet that’s heavily restrictive of carbohydrates.
| Micronutrient | Common natural sources | Fortified sources |
|---|---|---|
| Folate (Vitamin B9) | Asparagus, leafy green vegetables, legumes | Enriched breads, fortified cereals, fortified pastas |
| Magnesium | Leafy green vegetables, whole grains | |
| Potassium | Bananas, potatoes, spinach, tomatoes | |
| Vitamin C | Bell peppers, broccoli, brussels sprouts, kiwi, oranges, strawberries | |
| Vitamin E | Green leafy vegetables | Fortified cereals |
| Vitamin K | Broccoli, collard greens, kale, spinach | |
| Zinc | Legumes, nuts, seeds, whole grains | Fortified cereals |
Source: USDA & NIH Fact Sheets
Can carbohydrate-rich foods be sources for protein?
Plant-based proteins aren’t just for those electing to have a diet free of animal-based proteins. Globally, people get about 60% of their total protein intake from plant-based (and generally carbohydrate-rich) sources, and even in the United States, about 30% of total protein intake comes from plant-based sources.
While animal-based protein sources often provide more total protein per calorie, it’s important to recognize the contribution of carbohydrate-rich protein sources to total protein intake.
Protein content in common carbohydrate sources
| Food item | Calories per 100g | Protein (g) per 100 calories |
|---|---|---|
| Mushrooms | 22 | 14.09 |
| Soy | 446 | 8.19 |
| Lentils | 116 | 7.76 |
| Black Beans | 130 | 6.85 |
| Chickpeas | 164 | 5.43 |
| Whole wheat bread | 247 | 5.26 |
| Oats | 389 | 4.34 |
| Wheat | 339 | 4.13 |
| Quinoa | 120 | 3.67 |
Source: USDA FoodData Central
Note: These values vary based on the measurement and source of the item.
What are good carbohydrates sources of dietary fiber?
Carbohydrate-rich foods are also where we get most of our dietary fiber. Different organizations provide various fiber intake recommendations, but the World Health Organization (WHO) suggests that adults consume 25-30 grams of fiber per day, and the USDA recommends aiming for 14 grams of fiber for every 1000 calories consumed. Although fiber supplements are available, it is generally ideal for fiber intake to come from whole foods that also provide micronutrients.
| Food | Fiber (grams per 100 calories) | Notable micronutrients |
|---|---|---|
| Bran (wheat) | 24.0 | Iron, Magnesium, Selenium |
| Bran (corn) | 22.0 | Iron, Magnesium, Selenium |
| Mustard greens | 12.2 | Vitamin K, Vitamin C, Vitamin A |
| Collard greens | 11.5 | Vitamin K, Vitamin A, Calcium |
| Seaweed | 10.5 | Iodine, Vitamin K, Folate |
| Artichokes | 9.0 | Copper, Magnesium, Folate |
| Blackberries | 8.0 | Vitamin C, Vitamin K, Manganese |
| Lentils | 7.9 | Folate, Manganese, Iron |
| Chickpeas | 7.0 | Folate, Manganese, Thiamin |
| Raspberries | 6.5 | Vitamin C, Manganese, Vitamin K |
| Edamame | 5.2 | Folate, Iron, Manganese |
Source: USDA FoodData Central
Note: These values vary based on the measurement and source of the item.
Not getting adequate fiber can be a side effect of low-carbohydrate diets. Fiber intake can help with managing satiety and weight regulation. It also plays a significant role in controlling blood sugar levels and promoting digestive health. Moreover, a high-fiber diet can reduce the risk of developing several chronic diseases, including heart disease and type 2 diabetes. Therefore if taking part in a diet that’s heavily restrictive of carbohydrates, ensure you’ve planned for adequate fiber intake.
Why would people choose a lower-carbohydrate diet?
People opt for a lower-carbohydrate diet mainly to control body composition or because they believe it will positively affect their health outcomes. Restricting a macronutrient is not uncommon in efforts to improve or change one’s diet or body composition, and since carbohydrates aren’t essential nutrients, it’s a logical choice.
Carbohydrate restriction comes with a few immediate benefits for people. First, restricting any one macronutrient or category within a macronutrient (starches, added sugars, etc) can automatically make diet planning easier.
Additionally, people are often encouraged by the water loss associated with decreased glycogen retention (even though they can incorrectly associate it with fat loss). This is because carbohydrate consumption affects our total body water weight. Stored glycogen comes with 3-4 grams of water per gram of glycogen. How much muscle mass we have or other diet variables can affect this total amount. For example, muscle mass can store roughly 500g of glycogen, while the average liver stores 80g of glycogen. Additionally, those stats can fluctuate throughout the day. So, if you severely restrict carbohydrate intake, and your glycogen levels decrease as a result, you might see the number on the scale rapidly decrease by 1-3kg simply due to a loss in water weight.
Since we retain water with carbohydrate intake, restricting carbohydrate intake means we lose water during that restriction. However, if you return to a normal intake of carbohydrates, you will regain the water that comes with it. This can be one of the reasons people associate weight gain with carbohydrates, especially if they utilize carbohydrate-restrictive diets without the full knowledge of the mechanistic effects.
If you combine all of this with also restricting the high palatability factors of certain carbohydrates foods (leading to easy overconsumption), you have a logical recipe for why people would want to eat low carbohydrates.
How do carbohydrates affect performance?
Carbohydrates are pretty important for enhancing performance in certain training styles. While context is key when getting into specifics, it’s safe to say that carbohydrates help enhance performance for most people. Your body can release the energy stored in carbohydrates much faster and easier than it can release the energy stored in fat, helping you perform better during high-intensity exercise and fatigue more slowly during long-duration exercise.
The primary reason for this recommendation lies in understanding how glycogen is depleted and used in our bodies. Glycogen isn’t stored in a single compartment; it’s spread across multiple and accessed differently depending on training intensity and need. These compartments deplete at different rates. For instance, during a typical resistance training workout, whole-muscle glycogen might only deplete by 24-40%, but the intramyofibrillar glycogen can deplete more rapidly. Endurance exercise decreases these stores more aggressively, which is a predictor of time to exhaustion. In trained athletes, carbohydrate restriction has consistently shown to reduce glycogen stores and, by association, decrease overall performance.
Note that certain training styles and genetic setups can affect these things regardless of diet. Some training styles will affect stores more than others (e.g., low-volume resistance training will have less effect than endurance). That said, having carbohydrates in good supply doesn’t hurt if, in performance, we are discussing the ability to maintain energy levels in a given activity.
For most lifters and athletes, the default recommendation should be to include at least moderate levels of carbohydrates in the diet unless they have specific constraints or a strong personal preference otherwise. Carbohydrate intake generally enhances performance, and having a bit more is usually better than too little.
Does a low-carbohydrate diet affect muscle growth?
Growing muscle is more tricky, and there’s currently less cut-and-dry literature. I think a big reason for this is that so many factors increase muscle mass in the first place (i.e., enough calories, overload, experience, protein intake, etc.). By the time we reach carbohydrates, many pieces must be in place before that factor is examined. And even then, there isn’t always agreement on what low carbohydrates are, so it’s an area of study with many heterogeneity issues.
Studies where more aggressive carbohydrate restriction is used in both men and women have found that it provides suboptimal performance for muscle mass growth. Similarly, another study focused on natural bodybuilders found that while a very-low-carbohydrate diet can help during fat loss phases, it’s probably not ideal for hypertrophy. Slightly higher carbohydrate intake can increase lean mass (studies here and here), and the most recent meta-analysis on the topic found that ketogenic diets (very-low-carbohydrate diets) typically lead to slightly worse performance and fat-free mass outcomes.
While I don’t think the take-home is that you can’t build muscle while aggressively restricting carbohydrates, I do think from a logical approach, it’s easier to get the calories you need and assist in recovery with the use of protein and carbohydrates. It doesn’t necessarily need to be in a specific or short anabolic window. But since building muscle is already difficult, especially under natural circumstances, it’s best to cover your bases.
Is it sustainable to aggressively restrict carbohydrates long-term?
For some, eating a moderately low-carb diet is manageable if they naturally prefer fewer carbohydrates. However, this can be challenging for those whose primary nutrition sources are carbohydrates due to limited options, dietary choices like veganism, or personal preference. This difficulty is particularly pronounced for those who enjoy carbohydrates but have been restricting them.
Rigid dieting or adhering to restrictive dieting parameters has mixed long-term results. When discussing a standard lower carbohydrate intake, there is a higher likelihood of positive results or success compared to very-low-carbohydrate diets. However, once we move into very-low-carbohydrate diet restriction, diet adherence becomes a relevant issue.
One final point worth mentioning is that removing carbohydrates can sometimes lead to an increase in saturated fat intake. Increased saturated fat has been shown to elevate risks associated with undesired health outcomes. This can be avoided with education on diverse fat and protein sources as well as overall caloric balance. Still, it’s worth noting. Therefore, if you’re going to aggressively restrict carbohydrates for the long term, be aware of how to optimize the healthy factors of a low- to very-low-carbohydrate diet.
Conclusion
While carbohydrates are not considered essential nutrients because the body can produce glucose from non-carbohydrate sources, the role of carbohydrate-rich foods in providing energy, micronutrients, and dietary fiber is well-documented. Generally speaking, moderately low-carb diets can be effective for certain health goals and preferences, but people should be mindful and strategic when aggressively restricting carbohydrates. Very-low-carbohydrate diets could lead to nutrient insufficiencies and reduced exercise performance if not carefully managed. A balanced approach that includes an adequate amount of carbohydrates is ideal for most people.
