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

Saliva - a very useful fluid

A quarter of a century ago saliva was described as:
“ …not one of the popular bodily fluids. It lacks the drama of blood, the sincerity of sweat and the emotional appeal of tears”.

Despite that, saliva is critical to the taste of foods and the health of your teeth. The salivary glands are located near the back of the mouth (at the sides) and under the tongue, producing a fluid that is 99.5% water. It is the other 0.5% that is really interesting as that comprises sodium, potassium, calcium, magnesium, bicarbonate, phosphates, immunoglobulins, enzymes, mucins, urea and ammonia.

Saliva production is very individual, with 500–1500 mL (17-50 fl oz) produced each day, the highest flow being when eating. What does saliva do?
1. Lubricates your food. Try eating a sandwich without it.
2. Clears food from the mouth.
3. Remineralises the enamel of your teeth after each meal, snack or drink.
4. Has immunoglobulins that help kill evil bacteria and support healthy bacteria in your mouth.
5. Provide amylase enzyme to start breaking down starch in your food.
6. Provides a liquid mix to food so that taste buds can sense the flavours in your meal

If your mouth gets dry, the brain will direct you to go and get a drink. If your mouth is frequently dry, which can happen with some medications, over-enjoying alcohol, regular dehydration (eg athletes who lose a lot of sweat each day), then you lose the protective effect of saliva. Tooth decay, mouth ulcers, bad breath and difficulty talking are common symptoms of too little saliva.

So next time you have lunch, just for a moment, think “how sensational is saliva”. Then blow a raspberry. Can’t do that without saliva. You can have other fun with saliva, but we best stop right there. This blog still has a G classification.


Benn & Thomson 2014. New Zealand Dental Journal.

Wednesday, August 27, 2014

Calcium absorption

Calcium is a crucial part of the structure of bones and teeth. You knew that already. So how do you assess what food is a good source of calcium? You may just look for the number of milligrams of calcium there are in a serve, the more the better. Well that doesn’t always work as we shall see.

Or you could read some websites that give you counter-intuitive information, such as those claiming milk, yogurt and cheese being high in calcium, yet being a poor source of calcium. Let’s take a look at the data because Hannah Castledine, university nutrition student, was a bit annoyed when she went to presentation by a chef claiming that dairy just doesn’t cut it as a calcium source and we should rely solely on almonds and leafy vegetables.

Calcium absorption
During digestion the calcium is usually freed-up for absorption, although some calcium complexes can form which are difficult to absorb. That doesn’t mean that every atom of calcium gets absorbed into the blood. We still tend to absorb more calcium as more calcium appears in the diet, independent of its source.

At low amounts of dietary calcium, it is actively transported across the lining of the intestines and into the body. Once this system becomes saturated as we eat more calcium then the extra calcium is absorbed by passive diffusion.

Factors affecting calcium absorption
Vitamin D is needed for effective calcium absorption, and as you know many people are low in vitamin D. On average one in three adults are vitamin D deficient in North America, Australia and New Zealand, even more in the winter months.

Even if you get enough calcium in your food, a low vitamin D level is going to make it difficult to absorb enough. You will still absorb some calcium, but probably not enough for good bone mass.

As we get older our ability to absorb calcium declines, by about 1% every five years, with a slightly bigger drop in women at menopause. Hence, the reason for more calcium recommended for folk as they edge into their 60s.

The lactose in milk seems to give calcium an absorption “leg-up” by augmenting its passage across the intestinal wall. On the other hand, salt and caffeine can increase calcium losses through your pee. This is most likely to be a problem in people eating lots of salty processed food and gallons of coffee. If you eat well, avoid highly salted food and enjoy 3-5 cups of tea or coffee a day, then I wouldn’t change a thing.

Calcium sources
You absorb about 30% of the calcium from milk, yogurt and cheese sources, which is pretty impressive when compared to the 5% absorption from spinach. I mention this specifically because spinach is touted by the pop-nutritionist as a wonderful source of calcium. Much of the calcium in spinach is locked up in the form of calcium oxalate making it just too difficult to absorb. Same with the iron in spinach. Mostly bound to oxalate. As case of being high in calcium and iron but low in bioavailability.

I remember telling that to a men’s health group once, and one bloke did an air punch and said: “That’s going back to the missus”. I had to say that even if the calcium and iron in spinach goes down the loo it doesn’t make spinach a 2nd class veg – it is still high in folate and beta-carotene.

The calcium from Brassica vegetables is much easier to absorb. I’m talking broccoli, kale, bok choy and cabbage, for example. We can absorb about 50% of the calcium from the Brassicas, but beware that 1 cup of broccoli will have about 50 mg calcium (so 25 mg ends up inside you) while a cup of milk will have 300 mg calcium, with you absorbing about 90 mg of that.

If you don’t fancy milk, then I recommend you choose a calcium-fortified beverage in its place, such as a soy milk. How do you know if your milk substitute has added calcium? It will definitely be on the label. If there is no mention of calcium, then assume it is low.

I have previously written about food sources of calcium. Yes, almonds and tahini are other good sources of calcium, with 70 mg calcium in 30g almonds, and 30 mg calcium in a tablespoon of tahini.

The old days
Our ancestors may have got 1500mg of calcium each day through nuts, vegetables, seeds and beans, partly because they would be eating a lot more food than we do. Nowadays we do less activity, therefore need less food, so we need to make sure our food is high quality, and some of us will need to also make use of calcium-fortified foods.

What does it all mean?
I have tried to give you a fair and reasonable summary, free from food politics and bias. Yes, there are many who want to swing your views based personal nutrition evangelism. As you have heard many times from me, you are your own boss and your sources of calcium is your decision. If you are happy with dairy, then continue to make that a major source of calcium. If you are avoiding dairy for philosophical or allergy reasons, then there are other calcium sources.

Essentials of Human Nutrition, 4th edition p 142-145

Modern Nutrition in Health & Disease, 11th edition p 136-140

Wednesday, July 16, 2014

Gluten-free eating - when is it necessary?

When I was at dietitian school long ago we were taught that a gluten-free diet was only for those who had coeliac disease or an inflammatory skin condition called dermatitis herpatiformis. About one in 70 to 100 people have coeliac disease. The gluten triggers the immune system to breakdown the intestinal lining making it difficult to absorb the nutrients in food. That usually leaves you with uncomfortable intestines and difficulty in gaining weight or muscle.

Now it seems that gluten-free foods have become trendy. One US estimate is that one in 10 people have gone gluten-free at the moment. There are even supermarkets with gluten-free aisles (see the pic I took in Granada, Spain). Around 10% of all new food product launches around the world in 2013 were gluten-free. It is now a $5 billion global market, and just under $100 million market in Australia.
What is gluten?
Let’s clear up a few points. First know that gluten is a protein naturally occurring in grains like wheat, barley and rye. I had to point that out because there are some thinking that it is an evil additive or some toxin to be avoided. Not so. We’ve been eating it for millennia. The long, interconnected gluten proteins help bread to rise, providing the characteristic texture and springiness many enjoy.

Gluten-free does not mean “healthy”. Potato crisp/chips are usually gluten-free. Those gluten-free muffins are still high in Calories (fat and sugar are gluten-free). A diet without gluten might be a healthier diet if you are now eating more fruits, vegetables, nuts and legumes and dropped the croissants and donuts.

Gluten-free for weight loss?
If you are trying to trim up and decide upon the gluten-free diet as the way to do it, then you are likely to experience weight loss. That is not because gluten is fattening. It is because you will eliminate biscuits, cakes, pastries, bread (and therefore butter and margarine), pizza and most other take-aways, so weight loss and a better sense of well-being comes from an improved diet. This is the same reason why a low carbohydrate diet causes weight loss – many kilojoule-dense foods disappear and you are left pretty much with meat, fish and salad.

Non-coeliac gluten sensitivity
There may be people with symptoms similar to Irritable Bowel Syndrome who seem to respond to a gluten-free diet although they do not have gut lining atrophy on biopsy, yet they respond positively to a gluten-free diet or a wheat-free diet. It is not entirely clear if that is due to the gluten or to other compounds in grain such as fructans. If you have a science bent you may want to read a recent paper on the topic (use the link in the top right corner to download the full paper).

What does it all mean?
First, don’t go gluten-free just because your neighbour or best friend swears by it. If your guts are telling you that everything is not perfect, then see your doctor about testing for coeliac disease before you go on a gluten-free diet. If the test is positive, then a gluten-free diet is your solution. If the tests show that you do not have coeliac disease then see a qualified dietitian and do a proper trial on a gluten-free diet to see if symptoms improve. In this case, called gluten intolerance, you may find that gluten does not need to be totally eliminated, just reduced to a level that controls your symptoms.

CoeliacAustralia tells us that 80% of people with coeliac disease haven’t been diagnosed yet, which is 330,000 people by their estimate. You might be one of those that does feel better on a gluten-free diet, but make sure it is the lack of gluten that is making you feel better, not the lack of biscuits/cookies and cakes! If your guts are singing along beautifully then just eat well. And choose good quality gluten-containing foods.