Monday, April 27, 2015

Cooking oil: does heating cause health problems?

The thought comes up regularly – if you cook with oil does it lose all its healthy properties? Do unsaturated fats become saturated once they are heated? In other words should oil only be used for salad dressings? These are common questions. Let me try and make sense of this topic.

Frying oil at home
I have done a search of all the literature on cooking oils. OK, that’s a lie. I have actually read five extensive review papers on the effect of heating on oils. And they certainly tested out my chemistry. And none came to a simple solution to make my life easier. Let’s start with the one we can sort out quickly.

You may have heard that frying any oil will convert it to a saturated fat, making it bad for your heart. Let’s assume that you are referring to unsaturated cooking oils like olive oil or peanut oil (mainly monounsaturated), or safflower oil (mainly polyunsaturated). Let’s also assume you only use the oil once in frying, because you are using just enough to get the food cooked. What will happen during cooking? Nothing. The oil will remain pretty much as it was originally. Nothing I’ve read says any different.

Deep frying oil
Nevertheless, there is a potential problem when an oil is repeatedly used for deep-frying. I don’t know anyone who has a deep fryer anymore. We had one back in the late 60s for cooking chips (fries), fish and potato fritters. Don’t think it made it past 1975. So, I suspect the only source of a deep-fried food for any reader is from a fast-food venue.

Cooking oil at high temperatures for hours over many days does cause the fats in the oil to begin to oxidise (go rancid), which spoils the smell, taste and colour of the oil. When consumed, this rancidity can cause inflammation and damage to the artery linings and a rise in the risk of heart disease, including a rise in blood pressure. Long term heating also causes a loss of vitamin A and antioxidant compounds naturally present in oils like extra virgin olive oil.

How much cooking before an oil goes bad?
I would love to give you a specific cooking time that oils “turn bad”, but there are so many variables. Simply put, most studies show a decline in the oil quality (from a health perspective) after 5-10 hours of frying. The shorter time frame is for the polyunsaturated oils, according to the Heart Foundation. That means the once-off use of oil in cooking shouldn’t pose a problem, while repeatedly heated oil could be aging your blood vessels rather quickly.

The one thing nobody considers
When you buy your Extra Virgin Olive Oil do you ever give it a taste test (licking some off your finger)? If your olive oil was cheap-ish it is probably also old-ish, as in starting to go rancid. Now taste a good local olive oil. Probably full of fruit flavours. Dietitian Rosemary Stanton has written a lot on fats and has often said that European olive oil sold in Australia has been around too long and has rancid tones to its flavour. And she’s an official olive oil taster, so I’m going to believe her.

This is not just a problem in Australia and New Zealand. The Americans are being sold rancid olive oil and no-one seems to care.

Buying local olive oil is a good argument on many fronts - environmental, economic, and nutrition. There is plenty of great tasting oil in Australia, New Zealand and the US. No doubt the folk in Europe can get wonderful fresh Spanish, Greek and Italian olive oil.

What does it all mean?
Simple message – eat few deep-fried takeaways; enjoy more home cooking. (Note: some big take-away franchises use better quality oil, filter it regularly and top up with fresh oil, therefore lowering any health risk). When simply frying food, then purchase a cheaper unsaturated oil (eg Canola, Grapeseed). If you want some flavour in an Asian dish, then maybe some sesame oil. Save the top-end olive oil for the salad dressing or for drizzling on bread. Keep your oil cool, sealed and away from light, to slow down the oxidising process.

Santos CSP et al (2013). Effect of cooking on olive oil quality attributes. Food Research International 54: 2016-2024
Choe & Min (2007) Chemistry of deep-fat frying oils. J of Food Science 72: R77-R86
Stier RF (2013) Ensuring the health and safety of fried foods. Eur J Lipid Science & Technol  115: 956-964
Ng CY et al (2014) Heated vegetable oils and cardiovascular disease risk factors. Vascular Pharmacology 61: 1-9

Kefir: potential health benefits

Alberto Gómez from Buenos Aires wrote to me, wondering if kefir would be a useful sports drink. Well, I had never heard of kefir being downed by athletes. In fact I had never tried it myself, so I was about to get an education in taste and knowledge. Where I live kefir, a yogurt-style milk drink, is not widely available but I did track down a version made on the east coast of Australia (see pic). The plain version is too acidic for me, but the honey version hits the spot. It is too thick to work as a sports drink, unless diluted with water which is likely to reduce its palatability. I prefer to have it on cereal after my early-morning cycle training.

Alberto had also heard that kefir had a range of health benefits. Well, being a milk base with added Bifidobacterium and Lactobacillus bacteria, there is no doubt it will be similarly nutritious as yogurt. It originated in the Northern Caucasus mountains of Russia, its name taken from Turkish meaning “good feeling”. The fermentation process is started by “kefir grains” which contain bacteria and yeast in a carbohydrate matrix of granules. The granules have a popcorn or cauliflower shape and are visible to the naked eye.

Bumping out evil bacteria
There is quite a bit of research on the potential health benefits of kefir, as you would expect with a fermented food. The kefir bacteria are able to attach to the intestine lining to effectively “bump out” the pathogenic bacteria. They seem to also produce compounds that kill the nasty bacteria. Kefir seems to be effective in stopping the growth of Helicobacter pylori, a particularly nasty bacteria that is linked to chronic gastritis, ulcers and gastric cancer. Some other results suggest that it helps lower blood cholesterol levels.

In the laboratory kefir are able to kill and slow down cancer cell growth, and enhance the immunoglobulins that help your immune system function well. Anyway, you get the picture. And you can see why there is a keen interest in kefir.

I’m not sure that I have been consuming anything close to the kefir they enjoy in Eastern Europe, which is meant to be a little bit fizzy. Still, whether or not it is going to add years or minutes to my life, I thank Alberto for introducing me to this quite delightfully tasting style of yogurt.

Guzel-Seydim ZB et al (2011). Review: Functional properties of kefir. Critical Reviews in Food Science &Nutrition

Nielsen B et al (2014) Kefir: a multifaceted fermented dairy product. Probiotics & Antimicrobial Proteins

Monday, January 19, 2015

Milk for rehydration

With warm weather and/or physical activity you lose perspiration, and the evaporation of the sweat from your skin cools the body. Before long, that sweat loss needs to be replaced. Water is good. You know from previous articles both coffee and tea can rehydrate the body. Sports drinks are specifically designed for rehydration, especially for athletes during sport.

After sweating did you ever consider a glass of milk for rehydration? Well, it is 90% water, just like fruit juice, so theoretically it should be a useful drink. Or, if you prefer, soy milk which is also 90% water. One Australian research group has just published their results on rehydration drinks.
Drink more fluid than you lose
If you perspire, say 1 litre (34 oz), it makes sense to drink the same volume to make up for the loss. Only problem is that the kidneys still want to make urine, so you might drink 1000mL of water and yet produce 350mL of urine, still leaving you 350mL short of the 1000mL replacement. This is why you hear coaches and sports dietitians encouraging athletes to drink more, 150% more, than they lost as sweat.

So what is happening here? If you replace sweat losses with just water it actually dilutes the blood because you sweat both water and salt, then replace it with just water and next-to-no salt. Not a problem for normal sweating as you will get your salt from the next snack or meal. If you sweat heavily, like in this study, then drinking just water dilutes the blood and the kidneys act to concentrate the blood by creating some pee. This is why sports drinks have some added salt – it helps you to retain more water absorbed from the gut, with less pee, after sweating.

The power of milk
This is where milk comes in. This was a study of 15 young males who were exercised until they lost about 2% of their body weight as sweat in a session on the exercise bike (that’s 1.5kg in a 75kg person; 3.3lb in 165lb). To rehydrate they were given either milk, soy milk, Sustagen Sport (a milk-based nutrition supplement), or the sports drink Powerade. The volume given was 150% of the amount lost as sweat, in other words, more than sufficient to replace sweat losses, on paper at least. The milk and soy-based drinks were chosen as their natural salts, sugars and protein all work to help retain the fluid in the body, meaning you produce less pee.

Sustagan Sport takes the title
 After drinking 1.5 litres of drink for every 1 litre lost as sweat the athletes were tracked for another four hours, taking blood and pee samples, while checking body weight. The least amount of urine production was after drinking Sustagen Sport, the flavoured milk-based supplement that is fortified with extra vitamins and minerals, and very popular with Australian and Kiwi athletes. Put another way, more fluid was retained from a flavoured milk supplement drink, making it very viable as a rehydration fluid.

In second place came milk and soy milk, with little to separate them. The sports drink was last, suggesting you need to drink much more than 150% of losses, probable twice as much, when replacing losses with a sports drink.

What does it all mean?
Remember, this is a study of fluid replacement after you have finished your workout. Let’s be very clear, water or a sports drink are still very good choices to have while you are perspiring. After the gardening, brick-laying, half-marathon or cycle training has finished there are other options to help replace the sweat.

What this study shows is that a milk-based drink will do an excellent job of replacing your fluid losses when the work is finished. After a long bike ride, I put the bike back in the shed, open the fridge and enjoy a coffee-flavoured milk (pictured). I’m getting:
  1. Fluid
  2. Carbs to replace my glycogen
  3. Protein to help repair any muscle micro-damage; and
  4. A great flavour
  5. And a nice change after 2-3 litres of water on the bike.
Try it and see what you think.


Desbrow et al (2014) Applied Physiology, Nutrition & Metabolism 39: 1366-1372

Cow blowing (insufflation) to encourage milk letdown

So, I’m reading this book on milk (Milk: A global history by Hannah Velten) when I come across this picture on the right and I’m thinking “OK, this is looking a bit strange, and is surely quite disconcerting for both species.”

The photo was taken in 1982. It is a young lad blowing, via a tube, air into the vagina of a cow to induce milk letdown. I have read that similar result can be achieved by blowing air into the anus.

I know what you are thinking:
1. No, no, no, you are kidding me, right? No. It’s true, and it’s called “cow blowing” or insufflation. It has been described in many parts of the world, and the “art” has been around for a long time. Back in 440 BC a bloke called Herodotus described this in horses: “... they insert a tube made of bone and shaped like a flute into the mare’s anus, and blow; and while one blows the other one milks.”

2. OK, who was the first person to think of this?
“Hey Dad, Daisy won’t let down any milk, what should we do?”
“Have you tried scratching behind her ear?”
“Yes. Didn’t work.”
“What about rubbing her tummy”.
“Doesn’t work either".
Dad, stuck for ideas, decides to play a joke on the kids. “Try blowing air up her backside.” And so the incredible discovery began.

Seriously, I would like to know the physiology behind this practice, but I had difficulty getting an answer. Is it a physical response or does the air stimulate the release of oxytocin? Anyway, there is a fascinating, although long, history of insufflation of cattle here. There is also a short TV news video here. When food is not always easy to come by you have to admire human ingenuity to get nutrition.

Thursday, November 20, 2014

Taste buds - more than just about taste

A reader asked me the question “What happens to your taste buds as you age?” Well, I said (and assumed) that they decline with age. I remember my grandmother sucking on mints that were a bit too strong for some punk kid in his first decade. Anyway, I said I would find out more. And indeed I did. Come with me and I’ll guarantee you will learn something new.

Taste buds on the top of your tongue
My physiology text tells me that there are 10,000 taste buds in your mouth, with most concentrated on the top of your tongue. Each taste bud has a small opening called the taste pore through which liquids can come into contact with the taste receptor cells (see pic). That means you can taste soup or ice cream instantly, but a dry food will need the assistance of saliva. Most taste buds have a life span of just 8-12 days, so they are replaced three times a month.

You will have been taught that we have taste buds that sense the sweet, sour, salty and bitter tastes in food. You may also know that there is a 5th taste known as umami, the savoury flavour. There is even a suggestion of a 6th taste, one of a metallic sensation, partly because sometimes this is picked up in tasting labs for new processed foods and we don’t like anything that tastes ‘metallic’.

The chemistry of taste
In general, the sweet taste comes from sugars (obviously), alcohol and small proteins. The most famous example of the latter is the sweetener aspartame, which is a very small protein of two amino acids. Those two amino acids (aspartic acid and phenylalanine) are abundant in nature but still people consider them to be “artificial” and the downfall of western civilisation.

Salts, not just sodium chloride (table salt), are salty, and acids tend to give an sour flavour (eg citric acid in lemons, and compounds in spoiled foods). Many poisons in nature taste bitter, so it is speculated that the bitter sensation is to help us avoid becoming sick, as well as avoiding cabbage. Certain amino acids, like glutamate, provide the umami or savoury flavour. They are abundant in mushrooms, tomato paste and parmesan cheese.

Weird stuff
Taste receptors aren’t just in the taste buds in your mouth. They are all through your digestive system, your throat and lungs, and (if you have them) your testis. No, I’m not kidding. OK, what is going on here?

There are proteins in saliva that mediate the taste of bitter, sweet and umami. The compounds in food that trigger the bitter taste also seem to trigger the process of expelling things from the body. Give an infant a bitter food and it will be spat out. Even if as an adult you can handle some bitterness, the taste can evoke sneezing and coughing.

OK, that makes sense, but taste receptors (not taste buds) in the testis and sperm? Look, I can’t say I fully understand, although it seems that the receptors may sense a wholesome diet in Dad meaning there is abundant food, or sense toxic substances in Mum, suggesting she may not be ready for pregnancy, signalling sperm death. So, these receptors could be sensing the health of prospective parents. Weird, but seriously cool if that be the truth. (Here, I have taken artistic license; you read the paper and see if you can make better sense of it. Warning: It contains sentences like this: “Odorants directly activate CatSper without involving GPCRs or cAMP”).

Sweetness about bitter
The ability to taste certain bitter compounds is genetically based. Now there is a strong suggestion the bitter taste is also linked to longevity. The early evidence is that those of you who enjoy bitter tasting vegetables may live longer, no just due to the nutrition in a cabbage or Brussels sprouts. There are compounds in bitter fruits and veg that could be defensive against cancer and that puts the life odds in our favour. Some people have one specific gene for bitter tasting that is strongly associated with a long life.

Taste buds & aging
And speaking of a long life, let’s return to the original question: “What happens to taste buds as you age?” Certainly there is agreement that taste sensitivity declines as we age. A taste has to be stronger at age 75 than at age 25 before it is detected or recognised. Most studies agree that the salty and bitter tastes decline more than sour and sweet tastes over a lifetime.

As we age we seem to have fewer taste buds and fewer taste cells in each taste bud, with the biggest decline in the 74-85 year olds. Why this happens is not clear although there is suspicion that age might affect the stem cells involved in taste bud generation. 

What does it all mean?
Discover your taste buds. Eat a wide range of wholesome foods that take all your taste buds through a full range of experiences. Beats me why so many people rely on a hard-working teenager to cook them a predictable fare of fat, salt or sugar-laden easy-to-chew fast foods.

This was going to be a short article providing a simple answer to a simple question. But I learned so much more, and I hope that you didn’t mind me sharing it with you.

Sherwood L. Human Physiology, 6th edition p 221-225
Ross A et al. Modern Nutrition in Health & Disease, 11th edition p 577-579
Feng P et al 2014. Chemical Senses
Kinnamon SC 2012. Acta Physiology

Campa D et al 2012. PLoS ONE