Leucine: food sources and how much do you need?
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Leucine (pronounced loo-seen)
The internet is abuzz with chat about leucine so I thought it timely to add to this nutrition subject.
It is rare for me to single out one nutrient but today I have sharpened the focus on leucine, one essential amino acid that is known to play a key role in keeping muscles in great condition. You get leucine from food but not all foods contain it.
What is leucine?
Leucine is an essential amino acid. Essential amino acids (EAAs for short) are the basic raw materials that build protein structures of the body including the heart and muscles that support the body’s movements.
Humans can not make EAAs. Every person needs to consume them from foods and drinks that are rich in protein but here’s the catch. Just because a food is rich in protein doesn’t mean it contains all EAAs. The protein in most foods lacks one or more of the EAAs.
Because not all foods with protein contain leucine, you can’t simply look at a food label to choose an item with the most protein, and that’s where this article comes in to help.
Rather than complicate your everyday food choices, I have done the work for you and researched food composition databases from Australia and beyond to create a list of leucine-rich foods. You will see which everyday foods and drinks are richest in leucine.
Why the fuss over leucine? Why is dietary leucine important?
The spotlight is on leucine because it is important in preserving and building muscle. Loss of skeletal muscle and strength (sarcopenia) generally begins at around 50 years of age and was considered ‘part of getting older’ but you can work to preserve and protect your muscles. Loss of muscle and strength also happens at any age when sitting dominates the day.
Now is the time to adjust your dietary choices to help preserve and build muscle mass and maximise health reserves. You want to maximise your health and fitness efforts now before time ticks away. There is no escaping time… everyday we get older and then suddenly overnight (or at least it seems that way), age lines deepen, hair is grey, and you’re not as naturally strong and agile as you used to be.
If you don’t make some lifestyle and dietary tweaks now, as the decades fly by, you will be physically weaker, feel frail, balance poorly, and be at risk of falls, broken bones and other medical mishaps.
And regardless of age, if you are frustrated at your slow progress in gaining muscle strength after exercising or working out at the gym it could be that your training recovery plan is not timed well.
One tweak to focus on is the quality and timing of protein foods and drinks you consume.
For active people:
Muscle repair and growth responds best to food within the first 60 to 90 minutes after exercising. Including leucine rich foods could make a positive difference to this process.
Research with active older adults, proposes that recovery protein taken earlier, as soon as possible, after exercise maximises muscle growth.
Regardless of age, I suggest starting to eat or drink by 15 to 30 minutes after training but if eating too soon makes your body feel uncomfortable, aim to eat well before 90 minutes has passed.
Whether you have something in addition to your usual intake or do not add anything extra depends on your goals.
If weight gain is important, add something extra to your usual dietary intake.
If weight loss or maintenance (avoiding weight gain but gaining or preserving muscle) is important, stick with your usual intake and simply shuffle your usual foods and drinks around rather than add more. For you, this will mean timing exercise to finish just before a meal or shifting foods from a snack- or meal-time to be eaten after exercise.
There appears to be no benefit in loading up the evening meal with a large protein serve unless it is immediately after your exercise session. It is far better, to spread your protein intake across the day. The EAAs remain circulating in the blood stream ready for use.
For less active people:
For those who do not train or do not have intensive exercise sessions, the research about timing of protein intake is suggestive of a flexible approach.
You can choose to either evenly spread your leucine-rich protein intake across three mealtimes OR load up and consume the majority (70 to 80%) of your protein at lunch time.
If you are 65 years or better, pay special attention to the lunchtime meal and make sure it contains enough protein and, in particular, leucine-rich protein. This approach helps preserve muscle mass and, on the background of increasing activity, helps build muscle.
How much leucine is enough? How much do you need?
When it comes to nutrition many questions have incomplete answers. This is one of them.
Science does not know the full answer.
In trials with younger adults using leucine supplements, an amount equal to about 55 mg leucine per kg body weight per day is recommended. For example, for a 70 kg person, this equals 3850 mg (just short of 4 g) daily.
Too much leucine is not a good thing as it can cause a build up of ammonia in the blood which may lead to neurological problems. Too much is 500 mg (0.5 g) per kg body weight per day. For example, for a 70 kg person, a daily supplement totaling 35000 mg (35 g) is far too much. This dose is considered unsafe. Do not take leucine supplements without advice from your own dietitian or sports scientist.
In older adults, maximal Muscle Protein Synthesis is achieved after consuming 30 g of high quality protein which includes about 2.8 g leucine. This can be sourced from food rather than from a supplement.
The international guidelines from the PROT-AGE Study Group draw on this knowledge to propose a target of 25 to 30 g protein with 2.5 to 2.8 g leucine within a meal. This is a generalised population target for older adults only. Your individual needs may be different depending on your age, body weight, health and exercise pattern.
For most healthy people, it is possible and preferable to source leucine-rich protein from real everyday foods.
For a few people, additional supplemental protein boosted with leucine is necessary. Discuss your personal needs with your dietitian and doctor.
The top 5 leucine sources from within each food category are listed along with some other everyday popular items, for comparison. These are all energy equals as outlined in ‘this=that: a life-size photo guide to food serves’.
The numbers shown are approximate, rounded up or down for easier maths unless the leucine number is less than 0.1 or the total protein is less than 1.
To dive deeper, consider picking up my more comprehensive leucine table. You will not find these tables anywhere else because I have created them for you.
| MEATS (600 kJ per serve) | serve size | leucine (g) | total protein (g) |
| prawns | 18 - 20 medium | 2.5 | 32 |
| lean pork (fat trimmed off) | a small pork steak (around 90 g) | 2.5 | 30 |
| skinless chicken thigh | half a chicken thigh (around 90 g) | 2.5 | 30 |
| fish poached, seamed or baked | 1 small fillet (around 120 g) | 2.4 | 29 |
| lean goat (fat trimmed off) | about 80 g | 2.3 | 29 |
| lean beef (fat trimmed off) | 1 small steak (80 g) | 2.1 | 26 |
| eggs | 2 medium | 1.2 | 13 |
| DAIRY (600 kJ per serve) | serve size | leucine (g) | total protein (g) |
| cottage cheese | ½ cup | 1.8 | 18 |
| skim (non-fat) milk | 400 ml | 1.4 | 15 |
| skim milk powder | ¼ heaped cup | 1.4 | 15 |
| evaporated skim milk | ⅔ cup | 1.6 | 15 |
| haloumi cheese | 58 g | 1.4 | 12 |
| regular (full fat) milk | 200 ml | 0.7 | 7 |
| cheddar cheese | a thick slice | 0.8 | 9 |
| BREADS, CEREALS & OTHER GRAINS (550 - 600 kJ per serve) | serve size | leucine (g) | total protein (g) |
| semolina (made on water) | ¾ cup | 0.5 | 6 |
| cooked polenta | 3 x 1 cm thick slices | 0.5 | 4 |
| corn tortilla | 2 small | 0.4 | 3 |
| boiled wild rice | almost 1 cup | 0.4 | 5 |
| pocket bread | 1 small or ½ large | 0.4 | 5 |
| wholemeal bread | 2 thin slices | 0.3 | 6 |
| boiled quinoa | about ⅔ cup | 0.3 | 5 |
| boiled brown rice | ½ cup | 0.3 | 3 |
| porridge (oats cooked with water) | ⅔ cup | 0.3 | 4 |
| FATS & OILS (600 kJ per serve) | serve size | leucine (g) | total protein (g) |
| pumpkin seeds | 2 flat tablespoons | 0.5 | 6 |
| peanuts with skin | 2 flat tablespoons | 0.5 | 6 |
| sunflower seeds | 2 flat tablespoons | 0.4 | 6 |
| peanut butter | 1 flat tablespoon | 0.4 | 6 |
| mixed nuts | 2 flat tablespoons | 0.4 | 5 |
| oil | 1 flat tablespoon | 0 | 0 |
| butter, margarine | 1 flat tablespoon | 0 | 0 |
| VEGETABLES (500 - 550 kJ per serve) | serve size | leucine (g) | total protein (g) |
| corn (off the cob, kernels, fresh, frozen or canned) | ¾ cup kernels | 0.5 | 5 |
| orange sweet potato | 2 thick rings | 0.2 | 4 |
| white potato | 1 medium | 0.2 | 5 |
| mixed ‘light’ vegetables (equals a serve of starchy vegetable) | 2 cups | 0.2 | 9 |
| taro | 110 g | 0.1 | 2 |
| LIGHT VEGETABLES & SALAD (90 kJ per serve) | serve size | leucine (g) | total protein (g) |
| green peas (fresh or frozen) | ½ cup | 0.3 | 4 |
| english spinach, cooked | ½ cup | 0.2 | 3 |
| brussels sprouts | ½ cup | 0.1 | 1 |
| pumpkin | ½ cup | 0.1 | 2 |
| cauliflower | ½ cup | 0.1 | 1 |
| carrot | ½ cup | 0.04 | 1 |
| lettuce | ½ cup | 0.01 | 0.25 |
| FRUIT (300 kJ per serve) | serve size | leucine (g) | total protein (g) |
| strawberries | 2¾ cups | 0.2 | 5 |
| loquats | 1½ cups | 0.2 | 3 |
| starfruit (carambola) | 2½ | 0.1 | 2 |
| figs | 2 | 0.1 | 2 |
| guava | 2 | 0.1 | 2 |
| red apple | 1 small | 0.01 | 0.5 |
| banana | 1 small | 0.06 | 1 |
| orange | 1 | 0.07 | 2 |
| RED EXTRAS (600 kJ per serve) | serve size | leucine (g) | total protein (g) |
| flavoured milk drink | ¾ cup | 0.6 | 6 |
| choc-coated almonds | 4 small | 0.4 | 4 |
| popcorn | 1 large bowl (4 ⅔ cups) | 0.4 | 3 |
| pretzels | 1 cup | 0.3 | 4 |
| vanilla ice cream | 2 small scoops | 0.3 | 3 |
| milk chocolate | 5 squares (25 g) | 0.2 | 2 |
| jelly dessert | 1 cup | 0.08 | 3 |
| sugar | 8 flat teaspoons | 0 | 0 |
If you prefer not to eat animal flesh or are vegetarian, here are a few other top sources of leucine and protein to consider:
| OTHER VEGETARIAN options (550-600 kj per serve) | serve size | leucine (g) | total protein (g) |
| ricotta cheese | ¾ cup | 1.1 | 10 |
| plain yoghurt (not fruity) | 1 small 170 g tub | 1.1 | 10 |
| lupin flakes | ⅓ cup (before cooking) | 1.1 | 15 |
| lentils, cooked or canned | 1¼ cups | 1 | 13 |
| firm tofu | 3 big cubes | 1 | 13 |
| red kidney beans, cooked or canned | ¾ cup | 0.8 | 9 |
| baked beans, canned | ½ cup | 0.6 | 7 |
NOTE: Because the FSANZ Australian Food Composition Database is sadly lacking and incomplete when it comes to the leucine content of foods, I drew on data from New Zealand, Italy, Canada and United States of America to fill in the gaps. I also predicted the leucine content of manufactured foods that had an identifiable core ingredient (such as custard and crumbed fish) by using the leucine content of the dominant ‘native’ core ingredients (in these example milk and fish). For those reasons, the tables are not recommended for use in research projects but are great for anyone seeking a general guide to the leucine content of foods. Information collated Aug 2022.
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