The Role Each Macronutrient Plays in Muscle Growth

The Role Each Macronutrient Plays in Muscle Growth

“Get your macros” is a phrase you hear bodybuilders say, although how much of each macronutrient you need for optimal muscle growth is a debatable issue. In case you didn’t know, a macronutrient are food component you need in your diet in substantial amounts, unlike vitamins and minerals that your body requires only in small quantities. When we talk about macronutrients, we’re referring to the “big three” – protein, carbohydrates and fat. Each of these dietary components can act as a fuel source for your body, depending upon the circumstances, and all of them play some role in muscle growth.

Macronutrient: Protein

It’s hard to talk about building muscle without focusing on protein. Amino acids, the individual chemical units that makeup protein, are what your muscles use for growth and repair after a workout, but proteins have other functions as well. For example, proteins are involved in:

Repair of a variety of tissues, not just muscle

Healthy immune function

Making enzymes and hormones that regulate almost every process that goes on in your body

Growth and development (in kids)

The amino acids from protein can also serve as an energy source, although it isn’t your body’s preferred source of fuel. Normally, your body derives less than 5% of its fuel from protein, but when you deplete muscle glycogen and liver stores during periods of long physical activity and calorie restriction, protein becomes a back-up fuel source. Your liver has the ability to convert amino acids from protein breakdown to glucose, which comes in handy in a time of fuel shortage. Where does some of that protein come from? From muscle tissue. That’s why you shouldn’t do a long exercise session in a fasted state. When your glycogen stores are low after a period of fasting, you begin breaking down muscle tissue to make glucose and enter a catabolic state.

How much protein do you need in your diet to promote muscle growth? Currently, the recommendations for healthy adults are 0.8 grams per kilogram of body weight. This is based on the quantity needed to keep an average, healthy person in “positive nitrogen balance.” If you’re physically active and do endurance or resistance exercise, you need more than this amount to repair muscle damage and to supply amino acids for muscle growth. Depending upon how much time you spend working out and the intensity of your workouts, between 1.2 to 1.6 grams per kilogram of body weight is adequate for most physically active people, although some sources recommend protein intake as high as 2.0 grams per kilogram. Unless you’re a heavy-duty bodybuilder, 2.0 grams per kilogram is probably overkill. When you consume this much protein, you’re leaving less room in your diet for the other macronutrients – fat and carbohydrates. The key is balance.

You can meet your protein requirements with animal and plant-based protein. Most plant-based sources of protein, with the exception of soy, are lacking in at least one essential amino acid. So, if you eat a predominantly plant-based diet, be sure to eat a variety of plant protein sources.

 Macronutrient: Carbohydrates

Carbohydrates are your body’s preferred energy source during high-intensity exercise. The excess carbohydrates you consume through diet are stored as muscle glycogen and liver glycogen. You often hear people, even athletes, extolling the virtues of low-carb diets, even very low-carb, ketogenic diets. Your body can adapt to some degree to this type of diet, but it isn’t ideal if you do high-intensity exercise, long periods of endurance exercise or resistance training because it will limit your performance. You’ll fatigue sooner due to low muscle glycogen stores. The amount of glycogen you store in your muscles is a reflection of how much carbohydrates you’re consuming in your diet. Eat a low carb diet and you’ll have less glycogen stored away in your muscles and liver.

Plus, dietary carbohydrates have a protein-sparing effect. When you have enough carbohydrate in your diet, your body doesn’t need to turn to muscle protein as a fuel source. Who wants muscle breakdown when your goal is to get more defined?

Overconsumption of the wrong kinds of carbs isn’t ideal either. Refined carbohydrates and low-fiber carb sources can cause problems with blood sugar control and insulin spikes that can make it hard to lose body fat. If you’re one of the 60% of overweight people who are insulin resistant, it’s even more important that you limit refined carbohydrates in your diet. The best carb sources are those that are digested and absorbed slowly, including non-starchy vegetables and some, but not all, fruits. Fiber-rich whole grains in moderation are another source of slowly absorbed carbohydrates.

What quantity of carbs do you need in your diet? The National Strength and Conditioning Association recommend that carbohydrates make up between 55% and 60% of a strength athlete’s diet. Other sources propose getting between 1 and 3 grams of carbohydrate per pound of body weight. How high or low you go will depend upon how intensely and how often you’re training.  If you’re trying to lose body fat, you may want to take your carb intake a little lower, around 50% of your total calories.

Macronutrient: Fat

At one time low-fat diets were all the rage. Now, there’s more awareness of the essential role fats play in health and the emphasis has turned to choosing healthy fat sources. In fact, a certain amount of fat in your diet is vital to supply two fatty acids your body needs and can’t make – linoleic acid and linolenic acid. When people talk about the importance of getting enough essential fatty acids, they’re referring to your body’s requirement for these fatty acids. You need fat in your diet for a variety of purposes, including the absorption of fat-soluble vitamins. Without enough fat in your diet, you can develop a deficiency of vitamins A, D, E and K.

What about fats for muscle growth? Yep, you need them.  For one, you need fat in your diet to synthesize hormones, like testosterone, which help boost muscle protein synthesis. Plus, omega-3 fatty acids from sources like fatty fish have an anti-inflammatory effect. You know how sore you feel after working your muscles harder than they’re accustomed to? A study showed omega-3 fats help ease the symptoms of delayed-onset muscle soreness when you’ve worked your muscles hard.

Some research even shows omega-3 fatty acids enhance the anabolic response to resistance training, giving your muscle the extra boost they need to grow. As you know, exercise is a stressor on your body. Omega-3s may help to mitigate the stress response and reduce tissue damage.

Keep fat between 15% and 30% of your total daily calories. Choose monounsaturated fats from sources like avocados, olive oil and macadamia nuts, and polyunsaturated omega-3s from sources like fatty fish, flaxseed, and walnuts. Although saturated fats, most abundant in full-fat dairy and animal foods, have been demonized for years, the stance is slowly changing after research revealed they may not be driving force behind heart disease after all. Coconut oil is high in saturated fat, but it contains medium-chain triglycerides, which may have health benefits.

The Bottom Line

Extreme eating plans that severely restrict a particular macronutrient, like carbs or fat, isn’t healthy and isn’t conducive to building muscle either. Keep your diet balanced, and make sure you’re consuming enough calories to support muscle growth.



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