Research Review: Do veggies improve endurance? | Precision Nutrition

Research Review:
Do veggies improve endurance?

By Helen Kollias, Ph.D.

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Eat more vegetables. Preferably brightly colored ones — and if you had to pick only one color, go with green.

You eat a lot of vegetables? Eat more. I haven’t heard of anyone eating too much spinach, broccoli or kale.

“Gee, I really shouldn’t have had that pile of kale last night. I’m paying for it now.”

Never happens.

We all know vegetables are good for us. They have vitamins, minerals, fiber, antioxidants and phytochemicals.

Most are relatively low in energy compared to their volume. In other words, they fill you up without a lot of calories.

But could vegetables have other health benefits that we haven’t yet fully appreciated? Today’s Research Review suggests that veggies’ nitrate content may be another factor that improves health and athletic performance.

Nitrates

Nitrate (NO3) is a compound composed of nitrogen and oxygen, and it’s found abundantly in vegetables — indeed, about 80% of our nitrate consumption comes from vegetables.

Nitrate content
(mg/100 g fresh weight)
Vegetable varieties
Very low, <20 Artichoke, asparagus, broad bean, eggplant, garlic, onion, green bean, mushroom, pea, pepper, potato, summer squash, sweet potato, tomato, watermelon
Low, 20 to <50 Broccoli, carrot, cauliflower, cucumber, pumpkin, chicory
Middle, 50 to <100 Cabbage, dill, turnip, savoy cabbage
High, 100 to <250 Celeriac, Chinese cabbage, endive, fennel, kohlrabi, leek, parsley
Very high, >250 Celery, cress, chervil, lettuce, red beetroot, spinach, rocket (rucola)

Recent evidence suggests that nitrate may have effects on cardiovascular health as well as mitochondrial function.(1)

Mitochondria: The power generators of the cell

Back in high school you probably had to sit through a few lectures about “the cell” and its parts (organelles). Depending on how long ago high school was, you may remember mitochondria (singular: mitochondrion).

Mitochondria are one of the cooler organelles since they convert your food into usable energy (ATP) for the cell when oxygen is around. It’s similar to power generators that convert coal to electricity. Power generation is cool — that’s why you see nutrition bars named “The Power Plant” and not “Water treatment plant”. That’s also why mitochondria are cooler than, say vacuoles.

mitochondrion

Generally, endurance athletes like marathon runners and cyclists have a lot of mitochondria in their muscles compared to sprinters and weight lifters. If you want more mitochondria, doing endurance training is a good way to start collecting them.

However, let’s say you are already doing endurance training and want to find another way to get the mitochondrial edge on your competitors. Short of stealing mitochondria from other people, how could you improve your mitochondrial efficiency?

Research question

Can vegetables improve your mitochondrial performance?

The study in this week’s review found something pretty hard to do — it found that vegetables are even better for you than anybody thought.

Larsen FJ, Schiffer TA, Borniquel S, Sahlin K, Ekblom B, Lundberg JO, Weitzberg E. Dietary inorganic nitrate improves mitochondrial efficiency in humans. Cell Metab. 2011 Feb 2;13(2):149-59.

Methods

This study used 11 young fit men (25 years old, VO2peak = 56 mL/kg/min).

The study used a crossover experimental design: The men were given either a placebo or sodium nitrate (0.1 mmol/kg/day) for three days. The researchers were interested in the nitrate part of the supplement, which is a compound made up of nitrogen and oxygen.

After taking the placebo or sodium nitrate, the men biked with either 100, 120 or 150 watts of resistance (depending on how fit they were) for 10 minutes. After the testing, the men were given 6 days to recover and wash out any supplement before starting on the other supplement (sodium nitrate or placebo) that was the opposite from the first round.

Before the bike rides, the researchers took a muscle biopsy from the men’s outer quadriceps (vastus lateralis) . Generally, most exercise physiology experiments use the outer quad to biopsy because it’s easier to avoid nerves and blood vessels. Additionally, cycling uses the quadriceps muscle group a fair bit, so researchers can examine how the training affects that particular muscle group specifically.

The men were asked to avoid physical exercise, heavy activity, and nitrate-rich foods (vegetables, grapes, tea, alcohol, and cured meats) for 3 days while they received the supplement and before the testing.

Results

Increased nitrate and nitrite levels

The first thing the researchers had to prove was that eating sodium nitrate actually leads to more nitrate in the blood, otherwise there wouldn’t be much point to doing the rest of the study.

Since this study was published, you’d guess that yes, there is more blood nitrate after nitrate supplementation. You’re right! Plasma nitrate levels were 169µM (169 X 10 -6 M) compared to 27 µM — or a 526% increase!

Since nitrate (NO3) can be converted to nitrite (NO2), the researchers checked that too. Nitrite went up to 163 nM (163X 10 -9 M) from 35 nM or 366%.

Sodium nitrate supplementing for 3 days increases plasma nitrate and nitrite levels. Check!

OK, now we know there’s more nitrate and nitrite in the blood. But what does that actually do?

Oxygen use

The first clue about the role of nitrate was that the guys used less oxygen when they biked when on nitrate compared to placebo (oxygen used: 1.95 L/min placebo vs. 1.89 L/min nitrate). In fact, when taking nitrate, they did more work for a given amount of oxygen (69.3W/L/min vs 66.5 W/L/min).

Respiratory exchange rate (RER)

Another clue was that the respiratory exchange rate (RER – ratio of CO2 produced/O2 used) changed during nitrate supplementation.

Generally, the RER ranges from 1.0 when you use only carbohydrates to about 0.7 when you’re only using fats. During all-out, gut-busting sustained sprints, you can get over 1.0 as a result of anaerobic metabolism, but in this case the guys were working well within their aerobic comfort zone. The RER measurements showed that the men used less oxygen during the test when on nitrate because they were using more carbohydrates (0.883 during placebo vs 0.914 during nitrate).

However, changes in RER only account for some of this increased oxygen efficiency.

Muscle biopsy

Next suspect is the mitochondria in the muscle biopsy samples.

After isolating the mitochondria using a centrifuge — think of a very powerful spin cycle on your washing machine — the researchers did what amounts to a VO2 test. By measuring how much oxygen the mitochondria use, and how much ATP they produce, researchers can figure out their efficiency (oxidative phosphorylation efficiency; P/O ratio).

Nitrate supplementation seems to have increased mitochondrial efficiency, since the P/O ratio went from 1.36 in the placebo trial to 1.62 in the nitrate trial. Importantly, there were no more mitochondria during nitrate supplementation. What we’re seeing here is a change in mitochondrial quality, not quantity.

Like real power plants, mitochondria aren’t 100% efficient. It’s well known that mitochondria “leak” protons. Actually, about 25% of protons “leak” into the inner part of the mitochondria by passing the normal ATP-making step. More leaky protons means less ATP.

The term “proton leak” makes it sound like you should call a plumber, but it seems to be more controlled than protons spewing randomly into the mitochondria — though researchers aren’t exactly sure why we have proton leaks in the first place, considering that natural systems hate waste and are usually very tidy. Currently, many folks hypothesize that “proton leakage” helps keep us warm.

Eating nitrate made mitochondria more efficient because they were leaking fewer protons (about 45% less than the placebo). Nitrate — could it be nature’s duct tape?

Conclusion

Supplementing with nitrate for three days, using levels that you can get with eating 200-300 g spinach made male cyclists use less oxygen to do more work.

This improvement came mostly from improving the efficiency of individual mitochondria.

There may be other relevant factors involved. For instance, when we eat food-based nitrate, bacteria in the mouth and gut reduce nitrate to nitrite, which is then converted into nitric oxide (NO). NO signals smooth muscle to relax, which increases vasodilation (opening of blood vessels) and thus improves blood flow. In fact, 8th century Chinese doctors used potassium nitrate to treat cardiovascular disorders such as hypertension and angina (as well as garlic, which also improves NO production).

What does this all mean? If you plan to do any endurance type race I’d say chow down on at least a big container of baby spinach (312 g) for each of the three days leading up to the race, and see if you beat your personal best. Worst case scenario — you’ll eat a little more salad.

Bottom line

As if eating spinach wasn’t good enough for you here is one more reason: increased mitochondrial efficiency because of more nitrate. This means potentially more effective oxygen use and endurance performance.

Now, you may be thinking: I’ll just eat salami! Processed meats are preserved with sodium nitrate. But I don’t recommend hitting the deli counter hoping to get the same effect. You’d need to eat about 100 X the amount of spinach or 20 kg to get the same quantity. In addition, non-food forms of nitrate (such as fertilizer) may have adverse health effects. (2)

So, as always, get your vitamins and minerals the way that nature intended — via minimally processed whole food. Viva veggies!

Eat, move, and live… better.

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References

Click here to view the information sources referenced in this article.