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 4ºC 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 cliché – 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.

Food addiction

Many years ago I wrote a book called Diet Addiction on the premise that the western world seemed to need a diet book best seller every 6-12 months. We were addicted to diets. Relatives never bought my book. They would ring or email asking my opinion on Scarsdale, Blood Group, Cabbage Soup, or Atkins. I would tell them they didn’t work, but the Tuscany All Natural Easy Body Fat Stripping Chocolate and Beaujolais Diet Revolution was quite sensational. Each day you got a square of chocolate, half a glass of Beaujolais, a head of lettuce, as much tap water as you could drink, plus two hours of walking.

I was trying to make the point that when they bought a best seller they were buying a title, not sense; hope, not reality. Nobody cared.

Food addiction

If diets are not addictive, just temporarily persuasive, can foods be addictive? Although, there is evidence that the foods you really enjoy do trigger the release of endorphins in the brain to heighten the enjoyment or that the sudden removal of certain foods can cause withdrawal-like symptoms, you won’t find an academic saying food is addictive.

And there I’m wrong. Canadian academics have come out and said that some foods have similarities to drugs in that we actively seek tasty and kilojoule-dense foods, needing increasing amounts for satiety, and suffering withdrawal when on a diet that precludes these foods. Like drug withdrawal, there is a high incidence for relapse from dieting.

Food and drugs spark the brain

Brain imaging studies show that similar parts of the mesolimbic system are activated by food and drugs, both causing the release of dopamine and endorphins. The authors told me more I didn’t know. When some people have gastric surgery to combat obesity, they may transfer their food addictive behaviour to another addictive behaviour, such as gambling or compulsive spending.

Gee, no matter what happens, it is costing the addicted consumer a lot of money. Why won’t the body crave a really cheap addiction, like watching the sunrise each morning, or volunteering at a charity, or train-spotting?

Fat sensitivity

In this month’s British Journal of Nutrition, researchers from Deakin University in Australia found that some people are very sensitive to the taste of fat and this sensitivity makes them eat less fatty foods. In fact, the fat sensitive people ate fewer kilojoules and had a lower Body Mass Index. In other words, they were leaner. The evolutionary theory of food choice states that humans sort out high fat (eg seeds, nuts) and high sugar (eg figs, plums) foods because they provided more kilojoules per weight than leafy vegetables. This finding shows that not everyone prefers a high fat diet.

What does it all mean?

There are some people who will seek high fat foods and some who are satisfied with less fat in food. It could be that some brains are hard-wired to seek kilojoule-rich foods, possibly in those that also have a personality that thrives on food rewards or need to self-medicate through food when the going gets tough.

Democracy and freedom brings abundance and excess. Some bodies cope better than others. That might be why it is so difficult to work out who or what to blame for the podge – ourselves, food companies, the current government, or the “system”.

References:

Canadian medical Association Journal 2010; 182 (4): 327-328

British Journal of Nutrition 2010; March 3: 1-8

Calcium absorption

Try answering this question (it’s not a trick question):

From which food are we likely to absorb the most calcium per serve?

a. Milk, 200 mL

b. Soy milk (calcium fortified), 200 mL

c. Broccoli, 1 cup cooked

d. Spinach, 1 cup cooked

The answer is (a), but here is the bit I didn’t know. We absorb about 32% of the calcium in milk and around 25% of the calcium in soy milk, yet we absorb 60% of the calcium in broccoli. Despite some strange folk promoting spinach as a calcium source, we absorb only 5% of the calcium in spinach.

Although we absorb a higher percentage of calcium from broccoli, the reason milk wins is because of its high level of calcium in the first place. From the serves given, about 75mg of calcium from milk serve is absorbed, 55mg from soy milk, 24mg from broccoli and only 4mg calcium from a cup of spinach.

A cuppa and blood glucose

A. I had a query I was really hoping you could help me with; I have read that having caffeine with food raises the Glycaemic Index (GI) level. I never drink coffee but often have green tea with my breakfast, lunch and supper meals! Will the GI of the food be raised with green tea? Vanessa.

Q. There is no simple answer to this one Vanessa. There is more and more evidence that coffee, and now tea, is associated with a lower risk of type 2 diabetes. There have been small studies suggesting that caffeine may cause a slightly higher blood glucose after a meal but no health authority has suggested avoidance of caffeinated drinks in those with diabetes.

I am going to give the default answer: If you don’t have diabetes then 3-5 cups of tea or coffee a day is unlikely to upset blood glucose and may even protect you from diabetes. If you have diabetes, then you should still be able to handle 3-5 cuppas a day unless blood glucose monitoring suggests this is raising blood glucose too high. Oh, and you are one of the few people who realise that green tea has caffeine.

Yes, there is a cure for the hangover

Q. Just wondering if you have written lately on nutrition related hangover cures - fixes and fallacies? I have had many interested friends, colleagues asking, especially about the role of vitamin C and B's as well as questions relating to liver detoxification - the role of herbs and nutrients. Hannah

A. Yes, there is a cure for a hangover Hannah and it’s exceptionally effective. It is known on the market as “time”, the same cure for the common cold and youthful looks. As time can’t come in a capsule, and people love capsules, then the hype merchants fill capsules with herbs and vitamins. There is no evidence that vitamins or herbs will diminish the intensity or duration of a hangover, despite the associated hype. Some B vitamins will become deficient in chronic excess alcohol consumption so a supplement may reverse the deficiency, but it won’t reverse the brain and liver damage.

As alcohol causes excessive pee production, and therefore dehydration, the best advice is to drink non-alcoholic drinks spaced in between the alcohol to reduce dehydration and the headache that goes with it. If one of your friends does get hungover then the best anti-dehydrating agent to offer them is a sports drink. So, that’s it Hannah – time and water, or Gatorade.

No cold water with meals?

Q. I would be interested in your comments re the information attached, I believe it to have no scientific proof and to be both alarmist and misleading. Enjoy all that you talk about. It seems to be sound common sense and I use it a lot as one of the coaches for the Spanish National Flat Green Bowling Squad. Ruth

(Ruth had attached an article stating that we should drink warm water with meals because cold water “will solidify the oily stuff you have just consumed. It will slow down the digestion. Once this “sludge” reacts with acid it will break down (and) this will turn into fats and lead to cancer”).

A. Hola Ruth. Gracias para su pregunta. The article would have to be have written by someone who doesn’t understand digestion. Sadly, information given out by multilevel (or network) marketing companies is rarely based on science. They often provide misinformation to imply that a certain product they sell is required.

Once food is swallowed it quite quickly tends towards body temperature. Drinking cold water can be useful in hot weather as it helps cool the core body temperature. All the same, it too will get close to body temperature over a relatively short time. All fats and oils will generally be liquid at body temperature. Oil doesn't turn to fat. Oil is fat, 100% fat, by definition.

Humans have always done the smart thing - drinking warm fluids in cold weather and cool fluids in hot weather. Both hot and cool drinks are consumed around the world. Very hot drinks are linked to a mild increase in oesophageal erosion and possible throat cancer. I mean very, very hot. Cold water is not linked to cancer.