Popeye ate his spinach for strength, and generations of children were told to do the same. The spinach was a poor choice. Its calcium is locked up so tightly that people absorbed about 5 percent of it, against 27 percent of the calcium in milk, and its iron gives the body trouble too.
The cartoon sailor himself credited something else. In a 1932 strip he said spinach was "full of Vitamin A", and the plant form of vitamin A only crosses into the body with fat, so even Popeye needed butter on it.
What shares the plate with a food can count for as much as the food itself. Put eggs on a salad and you absorb several times more of the vegetables' colour compounds. Shake mustard over cooked broccoli and you get four times the good stuff. Pour tea with a steak-and-greens dinner and you lose a big share of the greens' iron. None of it needs a supplement, and most of it needs nothing more than knowing what goes with what.
What pairing can do
First, the old rule. "Food combining" says protein and starch must never share a plate. As a weight-loss plan it did nothing extra: people on it and people on an ordinary balanced plan with the same calories lost the same weight and saw the same improvements. Whether it helps digestion is another question, and I could find no test of it.
I eat plain meals myself, usually one main food in place of a crowded plate, and my gut is quieter for it. That's my own experience and no more, and Indigestion? Your Stomach May Need More Acid, Not Less makes the fuller case.
The pairing that changed history was a pairing with lime. Mesoamerican cooks soaked and cooked their corn in limewater, which frees up what the body needs to make niacin. When corn spread around the world without that step, pellagra followed, a niacin-deficiency disease first described in Spain in 1735. The food was the same, and the preparation decided whether it fed people or made them ill.
Day to day, pairing works at a smaller scale. A handful of nutrients need a partner to get through the gut wall, and a handful of foods get in each other's way. Knowing those few pairs will get you further than any chart of food groups.
Iron, the pairing that matters most
Spinach's iron reputation came from a measurement error, corrected in the 1930s, and the story that a misplaced decimal point caused it is a myth of its own. Iron comes in two forms, and spinach has the harder one. The iron in meat, fish and poultry is the haem kind, which the body takes up readily. The iron in plants, beans and fortified cereals is non-haem iron, and the body absorbs far less of it.
For plant iron, the right partner changes everything. Vitamin C and meat, fish or poultry eaten in the same meal can raise its absorption about fourfold. So the spinach in a steak salad gives up more iron than the same spinach eaten alone, and a squeeze of lemon helps too. That boost is about food. When 440 anaemic adults were split into iron tablets alone and iron tablets plus vitamin C, blood counts and iron stores recovered just the same in both, so the orange juice with the pill is a habit you can drop.
The wrong partner works just as hard in reverse. Served with a hamburger meal, one cup of coffee took 39 percent off non-haem iron absorption, and one cup of tea took 64 percent. It's the tannins and other plant compounds in the drink, and the more of them, the bigger the cut. Coffee drunk an hour ahead of the food left absorption alone, but an hour after it, the loss was the same. With low iron, keep tea and coffee well away from meals.
The chemistry is old. Mix iron salts with tannins and you get iron gall ink, Europe's standard ink for some 1,400 years and the one Leonardo da Vinci drew with. A cup of tea does a small version of that to the plant iron in your meal.
Switching to herbal tea won't get you out of it. With a bread meal, peppermint tea cut iron absorption by 84 percent, cocoa by 71 percent and camomile by 47 percent. Milk in the tea or coffee made little or no difference.
A meat-based plate has the edge here. The haem iron in red meat, liver and shellfish is hardly affected by what's drunk alongside it, and the meat itself helps whatever plant iron is on the plate. Not every animal food does that. When 70 volunteers were tested, beef, lamb, pork, liver, fish and chicken raised plant iron absorption two to four times, while milk, cheese and egg did nothing for it.
Your body keeps its own count as well. In 31 men measured over five days, iron absorption fell as their stores rose, until it did little more than cover daily losses, which suggests healthy people don't build up too much iron from food. Those with an inherited overload condition such as haemochromatosis are the exception.
Fat carries the colours
The deep colours in vegetables, the orange of carrots, the red of tomatoes, the green of spinach, come from carotenoids, and they only cross into the body dissolved in fat. When people ate a salad with fat-free dressing, the carotenoids that reached their blood were close to zero. A reduced-fat dressing let more through, and a full-fat one more again.
The amount counts for more than the type. When 29 people ate the same salad with small, medium or large amounts of canola oil, soybean oil or butter, the large amount got the most across, and the type of fat mattered less. Canola edged ahead of butter on two compounds, though not by a clear margin. So be generous, whichever fat you use.
Avocado works too. Added to tomato salsa, it raised the lycopene people absorbed 4.4 times and the beta-carotene 2.6 times.
Eggs do the same job and bring their own carotenoids along. Adding whole eggs to a mixed vegetable salad raised the absorption of the salad's own carotenoids three to eight times over. A salad with eggs and a proper olive oil dressing is worth far more than the same leaves with lemon juice alone. A good makes a dressing worth eating.
In much of Europe the tomato was first grown for show, because its nightshade relatives had people assuming it was poisonous. Cooking helps it as well. Lycopene from tomato paste was far more available than from fresh tomatoes eaten with the same oil, nearly four times as much overall, so a slow-cooked tomato sauce with olive oil beats a raw tomato salad for it.
The same rule covers vitamins A, D, E and K, all of which dissolve in fat. And the plant form of vitamin A isn't vitamin A yet. Beta-carotene has to be converted, and Why Eating Well Isn't Enough Anymore has the gene variants that cut that conversion by as much as 69 percent in the women who carry them. Liver, butter and egg yolk bring it ready-made.
In 17 people whose vitamin D levels had stalled on supplements, blood levels rose by more than half when they moved the pill to their biggest meal of the day.
Vitamin D also pairs with calcium. Calcium absorption was 65 percent higher when people's vitamin D levels were higher, even though both levels counted as normal. Calcium without enough vitamin D is a half-finished job.
Fish oil needs the same help. Taken with a high-fat meal, absorption from the common, cheaper form of fish oil tripled to about 60 percent, and even the natural form did better. With a low-fat meal, the same capsule delivered about a third as much.
Small tricks with big effects
Mustard on cooked broccoli. Broccoli's prized compound, sulforaphane, only forms when an enzyme in the raw plant gets to work, and cooking destroys that enzyme. Mustard seed carries the same enzyme. When people ate cooked broccoli with a pinch of powdered mustard, they absorbed over four times as much sulforaphane as from the broccoli alone. The word itself comes from the Latin mustum, grape must, which was mixed with the ground seeds to make the paste. Keep by the stove and it becomes a habit.
Black pepper with turmeric. Curcumin, turmeric's main compound, hardly reaches the blood when taken alone. Piperine, the compound in black pepper, raised its absorption by around 2,000 percent. That's a good reason to grind pepper over a curry. It's also a reason for caution with supplements that pair the two at high strength, because liver injury from concentrated turmeric supplements has been turning up more and more often.
Pairings that work against you
Tea or coffee with iron. The biggest everyday loss, covered above.
Spinach for calcium. Spinach is rich in oxalate, which locks its own calcium away. Boiling helps with the oxalate: spinach boiled for about 12 minutes lost around 60 percent of it, against 30 percent when steamed, and the lost oxalate turned up in the cooking water, so tip that out. That makes spinach kinder if you're prone to kidney stones, three in four of which are made of calcium oxalate. Calcium helps as well, because it holds oxalate in the gut: oxalate absorption fell from about 17 percent on a low-calcium day to 2.6 percent on a high-calcium one.
Spinach stays a poor source of calcium. Count sardines with their bones and dairy for that. Those bones do the job: in a small test, calcium from salmon and cod bones was absorbed at about 22 percent, against 27 percent from the calcium carbonate it was compared with. Spinach is the side, not the foundation.
Calcium pills with an iron-rich meal. Calcium blocks iron at the same meal, from pills and dairy alike. Yet raising calcium substantially for long periods left iron status unchanged, so the effect looks short-lived, and the body may well compensate. Dairy in the same meal is no cause for alarm. If your iron runs low, take a calcium supplement apart from your iron-rich meals.
Acid blockers and B12. Vitamin B12 in food is bound to protein, and stomach acid frees it. After two years or longer on the stronger acid blockers, known as proton pump inhibitors, the odds of B12 deficiency were about 65 percent higher. On a long course, ask for a B12 check, and leave any decision to stop a prescribed medicine to a qualified health professional.
Grapefruit with some medicines. This one was found by accident. In 1989, a test of how a blood pressure drug behaved with alcohol used grapefruit juice to hide the taste of the alcohol. In a follow-up test on six men, the same juice took the drug's level to nearly three times what it was with water, while orange juice did nothing. More than 85 medicines are now known or predicted to interact with grapefruit, and one whole fruit or one glass of juice is enough. Seville oranges, limes and pomelos do it too. If you take a prescribed medicine, ask a qualified health professional whether grapefruit is safe with it.
Coffee with a thyroid pill. Swallowed with coffee, thyroid hormone tablets were absorbed 27 to 36 percent less than with water. Taken with water and followed by coffee an hour later, they lost nothing.
Milk or yoghurt with some antibiotics. With ciprofloxacin, either one cut the amount absorbed by 30 to 36 percent. If you're prescribed an antibiotic, check the leaflet for what to keep away from it.
Fat-free dressings. They strip the point out of the salad. If you're going to eat the vegetables, give them fat to travel with.
Unsoaked grains and beans with a mineral-rich meal. Their phytate grabs zinc and iron before the gut wall can take them up. Soaking, sprouting and long sourdough fermentation lower it, and meat in the same meal helps. Why Plant Protein Delivers Less Than the Label Suggests, linked below, picks that story up. Zinc follows its own rules: phytate and soy protein block it along with iron, while calcium, tea and coffee mainly get in iron's way.
A plate that pairs well
Build it around meat, fish or eggs. Meat and fish bring the easily absorbed iron and zinc and help the plant iron alongside them, and egg yolks bring the fat that carries the colours. The Hidden Power in Every Bite, linked below, explains why a plate like that keeps you full.
Add the fat. Butter, olive oil, egg yolks or the fat on the meat carry the fat-soluble vitamins and the vegetable colours across. takes the heat of a hot pan without burning, which makes it ideal for searing meat and finishing the side.
Season with purpose. Mustard on the greens, pepper on anything with turmeric, lemon on the spinach.
Move the tea and coffee. If you drink them, have them an hour or more before a meal. An hour after eating still cut iron as much as drinking them with the food.
Keep water away from the plate too. One glass on an empty stomach thins stomach acid within a minute, and a stomach already short of acid has less to spare.
Take fat-soluble supplements with your biggest meal. Vitamin D and fish oil especially.
Same food, more value
The food on your plate only counts once it crosses into you. A few pairings decide how much does: meat or vitamin C with plant iron, fat with vegetables, mustard with cooked greens, and drinks kept clear of the meal. None of it costs more or takes longer. Popeye had the right food and the wrong partner: his spinach needed butter.
Start with tonight's dinner. Put the meat in the pan first, cook a side of greens in butter, and leave the cup of tea out of it.
Why do some meals keep you full for hours? The Hidden Power in Every Bite: Why Some Foods Fill You Up — the signals in every bite that decide how much you eat.
Counting on beans and grains for protein? Why Plant Protein Delivers Less Than the Label Suggests — what your body gets from plant protein, and what it misses.
Know someone with tea in one hand and an iron tablet in the other? Send them this. Moving the cup to well before the meal might do more than the tablet.
Tried something here, or got a question it didn't answer? Write to us at contact@allforlife.club. Your questions shape the next articles.
Disclaimer: This article is general information. For advice about your own health, talk to a qualified health professional, especially if you have low iron or take supplements or medicines.
Affiliate Disclosure: This article contains affiliate links. As an Amazon Associate, All For Life earns from qualifying purchases, at no extra cost to you. We only link to products we would recommend without the commission.
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