Diet-induced thermogenesis

Joel, a reader, wrote to me and asked which of the four macronutrients in food required the most kilojoules/Calories to be digested. The four macronutrients are protein, fat, carbohydrate and alcohol, the only ones that provide kilojoules/Calories in the diet.

His question related to the fact that we burn kJs to digest food, that is, you have to burn some kJs to actually digest and absorb the kJs used by your muscles, heart, brain, liver, kidneys, lungs etc. This is called diet-induced thermogenesis (DIT).

The textbooks will tell that an average 10% of ingested kJs form the DIT. For example, if you ate 10,000 kJs (2400 Cals) then about 1000 kJs will be used up to digest the food. So, which of the macronutrients “cost” the most kJs to digest and absorb?

  

And the winner is … 

It was the first time I had ever been asked that and I hadn’t clue, and that meant some detective work. You may have had your Basal Metabolic Rate (BMR) measured. After an overnight fast you lie very quietly in a room with no distractions, a pleasant temperature, breathing through a mouthpiece for 30 minutes. Clever people then determine how many kJs you need for your baseline metabolism to stay alive. The BMR is about 5% higher than your sleeping metabolic rate.

Now if you eat a meal and get re-measured under the same conditions you can work out from the difference how many kJs are needed to digest that meal. This time the test won’t be for 30 minutes because the process of completely digesting a meal and then absorbing the nutrients is likely to take 6 hours or so. Yes, you would have to pay me to do the experiment too. I mean, you can’t even watch telly during the test.

Although it would be nice to give you very precise numbers, nature is never that accommodating. Here is an approximation of the “cost” of digestion:

Fat: 0-3% 

Carbohydrate: 5-10% 

Protein: 20-30% 

Alcohol: 10-30%

Protein satisfies for longer

Mmm, so it doesn’t take much effort to digest fat. It is quite easy to break the bonds in a fat molecule and absorb the resultant fatty acids. Protein requires a bit of effort to break it apart with digestive enzymes before absorbing the amino acids. This may partly explain why high protein foods satisfy the appetite more than carbohydrate or fat.

Apart from digestion and absorption, where do the other calories go?

Just to complete the picture, aside from digestion, the rest of our kJs or Calories are burned to keep us alive (your BMR - heart beart, liver function, breathing etc.) and to keep us active (your daily activity: walking, running, popping off to the gym, cleaning your teeth etc). If there are any kJs left over, you know where they are stored.

Why do I keep mentioning both kJs and Calories (officially written with a capital C because it is an abbreviation of kilocalorie. Why don’t we therefore say Joules? Dunno, sorry). For those of you who went metric last century, or the one before, I remind myself that we have lots of good folk living between Mexico and Canada who still use Calories. Hate to leave them out of the conversation. Simply put, 4 kJs = 1 Cal. Close enough.

What does it all mean?

Not a great deal in reality. You don’t eat just a single macronutrient at a meal. It will be a mix of protein, fat, carbohydrate and alcohol if you have a glass of wine with the meal. Different combinations and different quality foods will take more or less time to digest.

You can bet that a meal of legumes, vegetables, mushrooms and nuts will take more kJs to digest than a donut, meat patty and a soft drink, even if they were matched for protein, fat and carbohydrate. I recently read that about 15% of the fat in nuts passes out the back end. That is fat neither digested nor burned, yet it is still “kJs in”.

The DIT is more an academic exercise than a guide to constructing your next meal. The figures are only approximations. Minimally processed foods are likely to require more energy to digest than a highly processed food. Anyway, thanks to Joel I’m a little wiser. Hopefully you are too. Eat well.

Selected references:

·      Westerterp KR. Diet induced thermogenesis. Nutrition & Metabolism 2004 

·      Shils ME et al. Modern Nutrition in Health & Disease 10^th edition p 143 

Time between meals & snacks

Lindy wrote to me and asked what are the optimal times of the day to eat and the intervals between eating. Now, I could press the “nutrition guru, read my bestseller” button and make stuff up to sound knowledgeable. Or I could tell the truth. Let’s see how you go with the latter.

The best time to eat is when you are hungry. Yes, a crazy concept, and it won’t catch on, but it seems to make physiological sense. Then stop eating when you are no longer hungry. Whether that is a snack or a meal.

This is radically different to the “Ooh, looks nice, must try some”, “Hey, 1 o’clock, burger time”, “Man, I’m chockers, couldn’t fit in another morsel” way of dining while we live in a society with abundant food available 25/8.

I am being serious. Your body knows the best time to eat and drink. Nature comes with a clever operating system, complete with two inbuilt programs called hunger and thirst. Standard in all primates. Quite brilliant really.

Yes, it is more complicated than that. There are people who don’t experience fullness and always feel hunger. There are environmental cues that stimulate us to eat, whether we are hungry or not. The sight of Chocolate Bavarian seems to be able to over-ride all appetite cues. However, if you feel you have control of your eating most of the time, then eat when you experience hunger and stop when the feeling goes away. This is likely to be before you are full. We don’t have to complicate the message any further.

Breakfast

Not long ago I was asked to review the science on the benefits of breakfast for a cereal company. Although it is a common truism that “breakfast is good for you” I wanted to know if it remains good advice. So I plunged into 30+ research papers to see what was agreed about the first meal of the day. Here is what I learned.

  

Leaner

Breakfast eaters are less likely to be chubby. And it doesn’t matter if you are at primary school, university or calling the shots from head office. That might be all you need to know to reach for the cereal bowl. So, why are breakfasters likely to be leaner? You can probably take a good logical guess at that yourself.

Breakfast eaters are more likely to be active and eat a decent diet for the rest of the day. No surprise there. If you are fit, you get more hungry and can’t bypass breakfast. It may also be that eating soon after arising helps regulate your appetite control hormones, normalise your blood glucose levels and improve insulin sensitivity. There is some evidence that a long fast leads to higher levels of ghrelin, a hormone that may stimulate hunger and overeating.

Lifelong benefits

Breakfast doesn’t just pay dividends in the morning; it seems to give a good return on investment at the back end of life too. Breakfast skippers have a higher total cholesterol, higher LDL cholesterol (the evil one), an extra 5 cm (2 inches) of belt leather needed and, in one US study, a 21% greater risk of type 2 diabetes.

Smarter

It seems that with breakfast, you are more likely to meet your nutrient needs for the day. This may be because most breakfast choices are nutritious. Many breakfast cereals are fortified with nutrients like iron and folate. Milk or yogurt adds calcium and riboflavin. Add fruit or nuts and there is vitamin C, potassium, fibre, and on it goes. Miss breakfast and those two biscuits with coffee at morning tea don’t exactly make up the loss.

A large Australian study from last year showed that breakfast was critical for school performance, boosting both literacy and numeracy skills, independent of the socio-economic group. This backed up a review of the previous 50 years of studies in school children. There is no doubt that breakfast is necessary to help you to learn new stuff. Usually not difficult with primary school kids because they wake up hungry. It is the upper high school kids we need to convince.

Breakfast habits changing

Twenty years ago just about every young kid ate breakfast, with only some older teenagers giving it a miss, rising to 15% of 19-24 year olds being breakfast skippers. Now we have nearly 1 in 4 of upper high school students missing breakfast, in Australia at least.

Two decades ago, over three quarters of adults ate breakfast. Now barely 6 out of 10 adults regularly eat breakfast, women being better than the menfolk.Why the decline? The most common excuse is “not enough time”, in other words not enough time to pour out cereal into a bowl, add milk and consume (Gee, that’s gotta take 6 whole minutes) or plonk two slices of bread into the toaster, shave/brush hair/pack lunch while you wait, then add peanut butter. Let’s see, that’s 7.5 minutes.

But then my concept of time and food differs to most people, a fact I accept and have resigned myself to, especially since the day I saw a line of cars outside the drive-thru section of a famous takeaway at 8 am on a school day.

What if you don’t fancy breakfast?

Don’t know how you can do it, frankly. Me? I can’t do without breakfast. No breakfast and I can’t do up shirt buttons, I squeeze Heel Balm onto my toothbrush and drive into oncoming traffic. I have a court order to eat breakfast by 7.30 am or face serving jail time.

You, of course, may be able to get away with it. Can I suggest that you at least have a banana, a yogurt or one of those breakfast drinks as you leave the house? With some glucose racing through your arteries you will make better decisions. Then, when you do feel hungry, eat smart, like choose a sandwich, fruit or a smoothie and not scarf some eye-level, salty, extruded snack from the vending machine. Just the term “extruded snack” should put you off.

What does it all mean?

It means what it has always meaned. Clever people eat breakfast and breakfast eating makes you clever. The evidence is pretty over-whelming.

There are plenty of choices to kick-start the day – breakfast cereals or muesli with milk, topped with nuts or a banana (my choice), wholegrain toast with peanut butter, poached eggs and mushrooms on toast, yogurt and canned fruit and you can think of more. If you buy your breakfast look beyond the cappuccino and croissant because you are worth a lot more than that. A lot more.

Selected references:

·      O’Dea JA, Mugridge AC. Nutritional quality of breakfast and physical activity independently predict the literacy and numeracy scores of children after adjusting for socioeconomic status. Health Education Research 2012; 27 (6): 975-985

·      Hoyland A, Dye L, Lawton CL. A systematic review of the effect of breakfast on the cognitive performance of children and adolescents. Nutrition Research Reviews 2009; 22: 220-243

·      Astbury NM, Taylor MA, Macdonald IA. Breakfast consumption affects appetite, energy intake, and the metabolic and endocrine responses to foods consumed later in the day in male habitual breakfast eaters. The Journal of Nutrition 2011; 141: 1381-1389

Philosophy of Eating 2

In a recent blog I offered a philosophy of eating and gave the right of reply to Don Ardell. Here are some of your responses with the odd comment from myself.

Hi Glenn

Thanks for the article on A Philosophy of Eating and the input from Don as well. I found it very insightful. I did really appreciate the section on positive eating. I am discovering for myself about emotional eating and the negative thoughts that pop up such as "I shouldn't be eating this" or "This is bad for me."

Just enjoying the food and being grateful for it was a great reminder for me when eating food. So thanks again.

Kind regards

Helen Williams

Thanks for your thoughts Helen. Appreciated. We all suffer from self-scrutiny. Even as a dietitian I sometimes think when I'm in the supermarket "What if someone I know looks in my basket now and sees full fat yogurt, or a chocolate?" Glenn

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Hi Glenn.

Great newsletter. Love how you are secure enough to include another’s point of view in your own newsletter. I have to say that I agree with most of what you write; but not all. I think Don has captured my thoughts well with – “I certainly agree that we should be positive about food, unless it's loaded with fat, sugar, toxic chemicals and tons of empty calories. Then I think a bit of negativity might go a long way toward quality of life outcomes.”

As a mother of a healthy and rapidly growing 4 year old boy, I have become acutely aware of the daily bombardment of our society with marketing ploys to sell ‘products’ that don’t even rate as ‘food’ – in my opinion. Many of these contain no nutritional value whatsoever and should not be allowed to pose as food. The hardest part is that there is a growing (literally) element of our society that condemns parents that don’t want to feed these ‘food alternatives’ to our children – saying that we are somehow depriving our children!

I don’t have any objections to the occasional treat of something delicious, home made, wholesome and probably laden with good fats and natural sugars. But that’s the problem – the frequency of these treats is becoming alarmingly often. Everyone that comes into contact with your child thinks there is no harm in giving them an occasional treat. The cumulative impact of these well meaning gestures means that your otherwise well fed child now has a weight problem.

Rant over

Anne Finlay

Love to hear a rant Anne. And you don’t want to agree with everything I say because I could be wrong and also impose upon your democratic rights. For example, if I ran the world, you would have to register to smoke or buy donuts with proceeds of your estate going to medical care. Hardly democratic. And I predicted that drive-through breakfast would never, ever take off. Got that wrong. Glenn

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Hi Glenn,

As usual I think you are pretty much spot on and wish only that you were the first “Minister for the Enjoyment of Food” in the next government. I have a further question rather than a comment. The new Dietary Guidelines have just come out. I have some real problems with the philosophy and emphasis inherent in the document and the accompanying resources. In particular it seems to come from the viewpoint that food is a medicine to be prescribed in a detailed dosage according to your age, sex and health status. Am I jumping at shadows? What do you think?

Cheers, Rex Milligan

Yes, dietary guidelines (and dietitians) do tend to get stuck into the 'food as nutrient source' argument, although the new Australian ones have put more emphasis on food. Despite there being some mention of cultural and family influence on nutrition, it would be quite stunning to read: 

“Think about what you eat, enjoy what you eat and take responsibility for what you eat.” 

Or 

“There is no good or bad food; it is the amount and frequency of consumption that determines its healthiness.” 

Except Krispy Kremes, of course, which are not food but an advance party of alien forms that will one day, without warning, enlarge inside consumers, burst out and take over. There was a movie about it once but we don’t have enough Sigourney Weavers to have a chance when it happens.  Glenn

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Hi Glenn

I just wanted to say my neck is a teeny bit sore from nodding in agreement at this newsletter. So much of what you say here matches my own philosophy of eating.

Most of all, I think the advice to be positive and RELAX is so important to remember. In the face of so many faddish diets and trendy ways of eating – cutting out grains, sugar, vegetable oils or whatever the next ‘evil’ food is – it’s easy to be drowned out when your message, as ours is, is simply that boring old ‘moderation in all things; no food is bad; and by the way, eat lots of veges’.

What strikes me is that so often the messages around the pop diets are so negative - you MUST give up this food; it’s killing you! – leading to a very black-and-white view of the nutritional world. It can feel to the average person when reading these books and blogs that if you don’t eat this way you are just another poor, less-evolved slob who’s been brainwashed by the evil establishment; poor you. I find myself wanting to say to the authors, often: “Relax! We’re talking about food, here”. Yes, it’s important, and it has a great impact on how we feel and how well we are. But it’s not life and death. It’s not air-traffic control. As you say, if you have a good diet and listen to your body, the occasional pizza won’t kill you.

Keep up the good work Glenn – I’d love to just pick this whole blog up and publish it, but perhaps instead I’ll quote bits of it and use it for inspiration for my own and my editorials and newspaper column if you’ll allow me.

All the best

Niki Bezzant

Editor,  Healthy Food Guide magazine 

Thanks Niki. You are welcome to use parts for your great magazine.

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Hi Glenn,

As a comment to your latest newsletter I would like to add that too many people these days eat because they feel they have to and do not take the time to enjoy food. Most days I see people walking around West Perth eating a pie/pre-packed sandwich etc on their way back to the office. Food always tastes so much better when we take the time to sit and enjoy what we are eating especially with friends.

I am also a firm believer that a bit of chocolate cake occasionally never does anyone any harm but it is better to have a good quality cake than a supermarket one which contains all the additives, preservatives and bulkers with no real chocolate (which is the thing that we really want). Boucla on Rokeby Road, Subiaco, Perth do a fine line in cakes!!!!

Julie Daws

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Hello Glenn,

I always enjoy reading your newsletter because the topics addressed are interesting as well as informative. Being a dietitian, I have always noticed that foods that are suppose to be eaten 'sometimes' have a negative connotation; however I strongly believe that these foods at least have a role in improving mental health (feels good to have fries/pizza). And if they are consumed occasionally/sometimes; while eating well otherwise/most of the times- there is no need to put negative emotion around it. Thus I second your point that if one is eating well most of the time + avoiding non-hungry eating = it will result into a healthy diet  (low GI, low sat. fat). 

Cheers,

Nisha Palan

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Think positive thoughts about food - it is for nourishment, socialising, sharing, culture, discovery etc. It will keep you alive. Be grateful.

Amen to that Glenn, it summarises all what food meant to be for humans.

Kind regards

Wafaa Beaini