1 September 2011

Food for Thought

Beat your metabolic rate and burn your fat stores – Prof Jennie Brand-Miller explains how

Jennie Brand-Miller
Prof Jennie Brand-Miller

Our genetic make-up underlies our metabolic rate – how many kilojoules (calories) we burn per minute. Bodies, like cars, differ in this regard. A bigger body like a bigger car requires more fuel to run than a smaller one. When a car is stationary, the engine idles – using just enough fuel to keep the motor running. When we are asleep, the ‘revs’ are even lower and we use a minimum number of kilojoules. Our resting metabolic rate (RMR) – the kilojoules we burn by just lying completely at rest – is fuelling our large brain, heart and other important organs. Although the number of kilojoules (the amount of fuel we use) increases when we exercise or move around, the greatest proportion of the kilojoules we use in a 24-hour period are those we use to maintain our RMR.

Since your RMR is where most kilojoules are used, it is a significant determinant of body weight. The lower your RMR is, the greater your risk of gaining weight – and vice versa. And here’s where your genes come into the story as they determine whether you have a high or low RMR – it one of those things that does run in families. We all know someone who appears to eat like a horse but is positively thin. Almost in awe we comment on their fast metabolism, and we may not be far off the mark.

Men have a higher RMR than women because their bodies contain more muscle mass and are more expensive to run. Body fat, on the other hand, gets a free ride. These days, too many men and women have undersized muscles that hardly ever get a workout. Increasing muscle mass with weight-bearing (resistance) exercise will raise your RMR and is one of the secrets to lifelong weight control.

Interestingly, we know that our genes dictate the fuel mix we burn in the fasting state (overnight). Some of us burn more carbohydrate and less fat even though the total energy used is the same. Scientists believe that subtle deficiencies in the ability to burn fat (as opposed to carbs) lie behind most states of being overweight and obese.

Indeed, in their latest research, if you have one copy of a high risk gene called FTO, geneticists have found you are 30 per cent more likely to become overweight. If you have two copies, then you are 67 per cent more likely! That is the strongest association yet of a common gene with obesity. Unfortunately, one in six people of European descent carry two copies and are therefore more prone to gain weight in the current environment.

This doesn’t mean that if your genes are to blame you should resign yourself to being overweight too. But it may help you understand why you have to watch what you eat while other people don’t. Furthermore, the current epidemic of overweight can’t be blamed on our genes – our genes haven’t mutated in a space of 25 years, but our environment has. So while genetics writes the code, environment presses the buttons. Our current sedentary lifestyles and food choices press all the wrong buttons!

If you were born with a tendency to be overweight, what you eat matters more. Genes can be switched on or off. By being choosy about carbohydrates and fats you will maximise your insulin sensitivity, up-regulate the genes involved in burning fat and down-regulate those involved in burning carbs. By moving your fuel ‘currency exchange’ from a ‘carbohydrate economy’ to a ‘fat economy’, you increase the opportunity of depleting fat stores over carbohydrate stores. This is exactly what will happen when you begin to eat a nutritious, low GI diet.

A bowl of fruit


Anonymous said...

my teenage daughter has metabolic sysndrome, which we now manage with a low gi diet, and a very sweet tooth. if i bake / cook with fructose (eg fruisana, which more or less behaves like sugar) what does that do to her insulin resistance? the chemistry of baking is beyond me

GI Group said...

Baking can be tricky when you want to cut back on sugar and refined flour. You might like to check out recipes in the various GI cookbooks that our GI Group has been involved with for sweet treats including the Low GI Family Cookbook, The Low GI Vegetarian Cookbook and the Low GI Diet Cookbook. The recipes in these don't use fructose -- but sweeten with a little sugar or honey and dried fruits and apple puree etc. They also use less refined flour and add rolled oats etc. There are also sweet treats in the Low GI diet for PCOS book. If you do want to use fructose instead of sugar, keep the moderate amounts (no more than 50g a day). Have you tried Logicane -- the low GI sugar on the market here in Australia?

Panic Attack said...

Jump starting the metabolic rate to make it faster is one of the things that is necessary. With all the diet pills and other weight loss products on the market, your approach is more sound. Losing weight with the use of your suggestions has more long term health benefits.

Anonymous said...

I'm 27 years old, 5'7", and 221 lbs. I have PCOS. A few years ago I dedicated myself to exercising and [what I considered] eating right. 4-5 times a week, I slowly jogged a mile and 1/2 at a pace of 4 mph. I was faithful to this lifestyle for more than a year but I never lost a pound or dropped a pant size.

I recently discovered the book "The Low GI Guide to Managing PCOS" and it has turned my life around. I've been working hard to get 4-5 servings of vegetables and 3 servings of fruit each day. I love the foods I'm eating and I feel awesome! It certainly takes more planning than before, but I realized that I was going 2-4 days without having ONE VEGETABLE! In 3 weeks, I've lost 5 pounds. I've tried many diets, weight loss supplements, and exercise programs in the past, and I'm so excited that I've finally figured out what works for me; managing my blood sugar and eating fruits and veggies. I've also noticed that on days when I don't eat right, I feel sluggish and bloated. When I stick to my fruits, veggies, grilled chicken, and fish diet, I feel so much better. I have more energy and feel like the weight is falling off.

Thank you, THANK YOU. I can't tell you how appreciative I am of your book. You've helped turn my life around.

GI Group said...

Re PCOS ... We are really glad that you have found our book so helpful and that following a low GI diet has made such a difference in managing your PCOS. It is this kind of feedback that makes our work so worthwhile! Kind regards, Kate and Jennie

Anonymous said...

I live in Nigeria and our staple food is gari made from cassava tubers after grinding, dying and frying it without oil. We eat it with soup made of vegetables, fish and small beef. I would like to know the GI of dried, processed cassava i.e. gari.

GI Group said...

Re gari -- we have sent your question to our experts and will post a reply here as soon as possible. So, watch this space.

GI Group said...

Re gari: Here's what we have found. There are two gari dishes in the GI database – one with a GI of 56 and the other with a GI of 49 – on balance we suspect your Nigerian dish described is probably low GI. But we can't be sure. You can check this out yourself at www.glycemicindex.com and then select the DATABASE.

There's also a British Journal of Nutrition article on cassava back in 1990 that suggests cassava may be high GI: "Glycaemic index of selected staples commonly eaten in the Caribbean and the effects of boiling v. crushing"

If we find out more we will let you know. Do go to the database.