Monday, April 26, 2010

Skeleton in deposit

Although osteoporosis appears later in life, the process begins during childhood. If there is not enough calcium and vitamin D in the diet or, in the case of vitamin D, insufficient sunlight exposure, then not enough skeletal bone is created during our schooldays. Our bones reach peak mass by the age of 30 years and thereafter decline. The rate of the decline is greatly dampened if adequate calcium is consumed, you remain active, don’t smoke and get all your vitamin D needs through diet or sunshine.

Calcium & vitamin D

Your recommended calcium and vitamin D needs increase as you get older to help forestall the brittle bones of osteoporosis. A greater calcium intake slows down the rate of bone loss in the later decades, while the kidneys become less able to activate vitamin D so more D is needed. High calcium foods usually have their calcium levels mentioned on the label. You need about 1000 mg of calcium a day when you are youthful, increasing to 1300mg a day when you head to the retirement village.

Calcium, where art thou?

You know about milk, yogurt and cheese. There is next to no calcium in butter despite it being a dairy food. Calcium is found in the ‘watery’ part of milk, not the fatty part we call butter. Some canned fish can provide calcium providing you eat the soft bones; think of sardines, pilchards, tuna and salmon. Don’t assume other ‘milks’, like soy and rice milk, have calcium unless they specifically state on the label that they are calcium fortified.

The list below shows you how many serves of selected foods you need to eat to get the same amount of calcium found in a serve of milk or yogurt.

Milk, yogurt, 200g [1.0 serve]

Cheddar cheese, 40g [1.0]

Broccoli, ½ cup [5.5]

Brussel sprouts, ½ cup [8.3]

Cauliflower ½ cup [8.6]

Canned sardines, 100g [1.1]

Sesame seeds, 30g [13.0]

Soy milk (unfortified), 250 mL [31.0]

Soy milk (calcium fortified), 250 mL [1.4]


You may recall that Annyca asked about the calcium in almonds. Although I knew their calcium content (about 70mg in a 30g handful) I wasn’t sure how much was likely to be absorbed. That took a little tracking down. Thankfully super-dietitian Helen Mair was able to help. She says you would need to eat about 170g of almonds to get the same amount of calcium as found in a 200 mL glass of milk. That’s about a cup of almonds.

What does it all mean?

Like so many aspects of health, it is what you do throughout life that minimises the risk of brittle bones. Waiting until the first hint of osteoporosis means leaving it too late. Women are more likely to get thin bones because they lose the protection of the hormone estrogen after menopause. In men, testosterone is the hormone that protects bone. Levels of testosterone tend to drop more slowly than does estrogen in women, where women can lose 20% of their bone mass in the decade after menopause. Think about your bones today.

Reference: Whitney & Rolfes. Understanding Nutrition. 10th edition 2005

Magnesium and fat and calcium

John asked if magnesium had to be present as well for calcium to be absorbed. We know that vitamin D helps calcium to be absorbed from your food. I checked the texts and there was no mention of magnesium being critical for calcium absorption. Some sources of calcium are also pretty good for magnesium too. A cup of reduced-fat milk has about 35 mg magnesium and 200g of yogurt has around 40 mg, about 10% of your daily needs.

Hannah asked if removing fat from milk, making it skim milk, had any effect on calcium absorption. Had to get the sniffer dogs onto that one too. The word is that the fat content doesn’t influence the amount of calcium absorbed from milk. That’s good news because skim milk generally has a higher calcium content, and less kilojoules, compared to full cream milk.

What a waste

Last week I was at the Public Health Association of Australia annual conference in Canberra. I want to tell you something interesting I found out.

Amy White, a postgraduate teaching fellow at Bond University in Queensland told us that around 10-30% of all bananas grown are simply discarded, basically at a loss to the farmer. The sad part is that four out of five discarded bananas are perfectly edible and ideal for consumption. So why do they get thrown?

In this game you need to be bent; straight ones never get to market. Even slightly bent ones won’t make it; you need to be properly bent, but not too bent that you horseshoe. No __double pups__, those bananas that are conjoined, the Siamese banana. No minor blemishes on the skin, little birth marks that don’t affect the flesh. No single or double bananas either. Bananas have to go to market in hands of 3-9 bananas. Yet how often do you, or others, grab just one or two bananas at the shop?

When next you question the cost of fresh produce just think of the amount that gets wasted only because major supermarket chains lay down the law on what is the “perfect” fruit or vegetable. Like humans, bananas come in different shapes and skins; it’s what’s on the inside that counts.

Wednesday, April 7, 2010

Enlightening vegetables

For the best retention of nutrients in vegetables, the common view is that they should be eaten as soon as possible after harvesting. Certainly, they don’t want to spend too long in the supermarket. That view may have to change, for spinach at least.

Photosynthesis continues under light

After harvesting, fresh produce is not necessarily “dead” or “dying”. A recent study by the US Department of Agriculture found there was a benefit to leaving spinach under supermarket lights.

Plants have two forms of chlorophyll, helpfully called A and B, one absorbing the blue/violet light and the other absorbing the red/yellow, while the plant reflects green light so vegetables like spinach look like spinach. The fluorescent lights used in supermarkets mimic the spectrum of natural sunlight. The light exposure, particularly in the blue and red range of the spectrum, allows the process of photosynthesis to continue, encouraging the production of vitamins, especially B vitamins.

Folate & vitamin C benefit

In the study, spinach was kept in clear plastic containers at 4ÂșC and exposed to light continuously for up to nine days. In that time the vitamin C levels rose over three days then returned to the original level over the next six days. When spinach is kept in the dark, folate levels decline by 30% in a week. This loss was prevented when stored under light.

All bio-active compounds benefit

Overall, spinach stored under continuous light had higher levels of all bio-active compounds compared to spinach kept in the dark. Senior research Gene Lester suggests that consumers should consider grabbing produce from the front of supermarket display cases that are kept under light.

I don’t think this research will make any practical difference to how you choose or store vegetables, except that you might now no-longer assume that supermarket fluorescent lighting, or even sunlight, causes nutrient loss. You should still be eating your veggies in the days soon after purchase. It is still wise to keep veggies in the fridge as the cool temperature slows nutrient loss and keeps them fresher for longer. Maybe the future will see the veggie crisper have a fluoro light.

What does it all mean?

There is am assumption that nutrient levels start declining once fresh produce leaves the farm. I have worked for three different fresh produce growers in the last five years. We know that fruit like bananas and avocadoes ripen after harvest without a significant drop in nutrition. Expose mushrooms to sunlight post-harvest and their vitamin D levels dramatically increase. And now we know that leafy veggies, like the spinach, continue to manufacture vitamins under fluorescent light.

Excuse the clichĂ© – nature is full of surprises, or, put another way, nature can make a mockery of your assumptions.

Reference: Journal of Agricultural & Food Chemistry 2010; 58: 2980-2987

More stuff you didn't know about calcium

Annyca asked about the calcium in skim milk and almonds. Before I respond to that, see how you go with this question.

Which has the greatest amount of calcium per serve?

a. Milk, reduced-fat, 200 mL glass

b. Yogurt, low-fat, 200 mL tub

c. Soy milk, 200 mL glass

d. Cheese, cheddar 30g slice

e. 30g almonds

(For our US friends: 200 mL = 7 fl oz approx; 30g = 1 oz approx)

The answer in my part of the world is (b) because:

A glass of reduced-fat milk has around 300mg of calcium;

200 mL low-fat yogurt (340-450 mg);

A glass of soy milk (60-230 mg);

30g cheddar cheese (200 mg); and

30g almonds (70 mg).

Previously, I told you that spinach was not a great source of calcium. That’s because the calcium is tightly bound to oxalic acid forming calcium oxalate, which cannot be split by digestive enzymes, therefore the calcium is not absorbed into the body. The same happens with the iron in spinach (it’s called ferrous oxalate). You get to absorb about 5% of the calcium and 2% of the iron in spinach. On the other hand, spinach is great for folate.

You will see from the figures I gave for soy milk that the calcium levels can range from 60-230mg in a 200 mL glass. Soy is not a good natural source of calcium. I suggest choosing a calcium fortified soy milk which will give closer to the 230 mg in a glass. A US study found that calcium in soy milk was absorbed only 75% as well as calcium in cow milk. It was not clear why.

Hannah and John had some questions about the type of milk. Skim milk in Australia generally has one and a half times more calcium than full cream milk. The fat in full cream milk (and any fat in your diet) may slightly reduce calcium absorption, so that could be an extra bonus in going for skim milk – more calcium and easier to absorb.