The amino acid leucine is of particular importance to female athletes. Leucine is one of the nine essential amino acids the body needs to obtain through the diet. Leucine along with other amino acids, are required for protein synthesis, tissue repair and nutrient absorption.
The demand for protein changes throughout the female hormone cycle. The fluctuations in estrogen and progesterone have a profound effect on muscle turnover and protein synthesis. Amino acids like leucine are harder to access during the high hormonal phase (day 12 to day 23 of a typical 28 day cycle). It is simply harder for females to build and maintain muscle during this hormonal phase making it even more important to ensure adequate intake of essential amino acids during this time.
Strength training including weights or resistance stimulates muscles to take up leucine (and other amino acids) and triggers muscular growth. Leucine can help prevent the deterioration of muscle with age so it is super important for masters athletes.
The richest sources of bio-available protein including leucine are in eggs, milk, fish, and meats. Milk contains both whey and casein protein. Whey is more easily absorbed and is higher in leucine than casein. Whey is also digested at a much faster rate than casein, ensuring blood leucine levels rise soon after ingestion and triggers protein synthesis responsible for building muscle. Hence why many athletes swear by chocolate milk as their preferred recovery drink. This is ok, but female athletes need additional leucine and would benefit from options such as a post workout smoothie including yogurt, milk, protein powder or almond butter. Recent research also suggests that the combination of other highly bio-available proteins rich in leucine results in more favourable muscle hypertrophy compared to other proteins such as whole milk protein, casein and soy protein.
But what about vegans or athletes with dairy issues?
Athlete’s who choose to avoid dairy need not feel they are missing out. Interestingly, a recent study found both whey and rice protein isolate administration post resistance exercise improved body composition and exercise performance with no differences between the two groups when taken in adequate amounts.
Leucine can also be found in plant based proteins included in soy, lentils, kidney beans, tofu, quinoa, hummus, rice, and almonds. These plant-proteins contain approximately 50% less leucine. Therefore vegan athletes need to pay attention to getting enough high-quality plant-proteins that offer the optimal amount of leucine (about 2.5 grams per meal or snack).
Vegans want to consistently enjoy soy, beans, legumes, seeds and/or nuts regularly at every meal and snack. Don’t have just porridge for breakfast; add organic soy milk and walnuts. Don’t snack on just an apple; slather apple slices with peanut butter. A blend of rice and pea protein powders makes a good substitute for whey based protein powders.
As a general guide 2 grams of leucine can be found in 120 grams beef, 130 grams almonds, 400 grams tofu, 3 eggs, 600ml cow’s milk or 900ml soy milk, 380 grams lentils, 350 grams kidney beans, 70 grams cheddar cheese, 350 grams yogurt, 27 grams whey protein isolate or 50 grams rice protein powder.
Elite high performance athletes with large volumes of training may struggle to obtain adequate leucine from their diet alone, especially if vegan. These athletes may consider using branch chain amino acid blends called BCAAs including leucine, iso-leucine and valine 30 minutes pre and post workouts in addition to a diet rich in leucine.
This table compares the leucine content of plant and animal foods.
Equivalent animal and plant sources of leucine
|Animal food||Plant food (swap)||Leucine
|Eggs, 1 large||Peanut butter, 2 tablespoons||0.5|
|Milk, ½ cup||Soy milk, low fat, 1 cup||0.5|
|Tuna, 25 grams||Black beans, 1/2 cup||0.7|
|Chicken, 60 grams cooked||Tofu, extra firm, 170 grams||1.4|
|Cheese, 14 grams||Almonds, 21 grams||0.3|
|Beef, 40 grams||Lentils, 1 cup||1.3|
Generally speaking, protein should account for 30% of your total daily energy intake. A gram of protein per kilogram of body weight is adequate for recreational athletes, while elite athletes may require up to 1.8 grams per kilogram of body weight, especially those in power and high-end endurance sports. On lighter recovery days protein intake can be reduced by 25%.
Consuming 20-25 grams of protein within 30 minutes of finishing a session is ideal for optimal recovery while having a protein rich snack at bedtime can boost protein synthesis by 22 %. You wake in a catabolic state after not eating during the night so having a protein rich breakfast is really important to restock your stores, fuel your daily activities and prevent overeating and sugar cravings later in the day.