Is Spinach the New Broccoli?

I have written enough about broccoli over the years that some readers tease me about it. Broccoli is, in fact, one of the few foods that earns the term superfood without much hedging. It has a reasonable omega-6 to omega-3 ratio for a plant, it is dense in fiber and minerals, and it contains two compounds, sulforaphane and indole-3-carbinol, that show up repeatedly in cancer prevention literature.

What is interesting, in the last few years, is that other vegetables are starting to earn similar attention as the nutrition science catches up.

The new entry. Dietary nitrate

Recent work on high-nitrate vegetables has identified a meaningful effect on muscle function and exercise capacity. The relevant compound is dietary nitrate, which the body converts to nitric oxide via a salivary and gastric pathway. Nitric oxide does several useful things, including vasodilation, improved mitochondrial efficiency, and modulation of muscle calcium handling.

The high-nitrate vegetables include spinach, beet root, Swiss chard, arugula, and certain lettuces. Note carefully that this is dietary nitrate, not the nitrites added to cured meats. The biology of the two is different.

What the studies show

Several intervention trials, mostly out of the UK and Scandinavia, have looked at beet juice and spinach in trained and untrained populations. The effects are modest but real. Improvements in time-to-exhaustion. Lower oxygen cost for a given workload. Slightly faster time trials. The doses that produced the effects ran roughly 6 to 10 mmol of dietary nitrate per day, which translates to about 200 to 300 grams of spinach, or two to three medium beets, or about a cup of beet juice.

The mechanism in muscle appears to be a combination of better mitochondrial coupling and more efficient calcium handling. Both are useful, particularly for older adults who are losing muscle mass and function with age.

What to actually do

Add spinach or beets to two or three meals a week. Do not stop eating broccoli. The compounds are different. The mechanisms are different. Both are useful. Older nutritional advice was largely about the macronutrient profile of these foods. The newer work on phytochemicals and their epigenetic and signaling effects is what makes them earn the attention.

Popeye was, in his way, ahead of his time. The mechanism just took eighty years to formalize.

— Doc