Food for thought: the science of eating a healthy diet

18 November 2016

In this podcast Chris is joined by Associate Professor Amanda Salis, who speaks about how to eat well in a world of confusing food and nutrition advice.

In this latest interview from the University of Sydney's Open For Discussion series, our host Dr Chris Neff explores the science of eating a healthy diet with Associate Professor Amanda Salis.

Almost every week it seems there’s a story in the news telling us about food and nutrition, and what we should eat to be healthy and avoid being overweight. But very often this week’s message contradicts what we heard only last week.

Is the so-called "paleo diet" appropriate for weight loss, or not? And while knowing what to eat for good health is one thing – but following nutrition and dietary guidleines may be a bigger challenge altogether.

Host: Dr Chris Neff
Guest: Associate Professor Amanda Salis
Producers: Dan Gaffney, Annika Dean, Vivienne Reiner, Verity Leatherdale
Editor: Caitlin Gibson

Associate Professor Amanda Salis
Amanda is a senior research leader at the University of Sydney’s Boden Institute of Obesity, Nutrition, Exercise and Eating Disorders based at the Charles Perkins Centre. She leads a research team that is unraveling the science of how our brains affect hunger, emotions and body weight.


Chris Neff: Just about every day we are told that some food is going to kill us, whether it’s cards or fats, or proteins or what have you…we are told each week that a different thing is going to kill us.

In this episode of Open for Discussion, we are going to talk with Associate Professor, Amanda Salis, who is a senior researched at The University of Sydney’s Boden Institute of Obesity, Nutrition, Exercise and Eating Disorders, based at The Charles Perkins Centre.

Today she leads a research team that is unraveling the science of how our brain effects hunger, emotions and body weight. Amanda, welcome to Open for Discussion.

Amanda Salis: Thank you

Chris Neff: Can you tell us a little bit about your research and what brought you to it?

Amanda Salis: So my research aims to find better ways for people to lose weight and keep it off throughout life. So what brought me to this area of research is personal dilemma basically; I was obese, severely obese in fact as a teenager and young adult and I was always struggling to lose weight. I mean, I could lose weight but I could never lose more than a few kilograms and it would just come back on, plus more. So, I knew there was something wrong with this whole idea of eat less, move more, and keep going until you get there. So that’s why I decided to start medical research to find better ways to help people to lose weight and keep it off.

Chris Neff: That’s brilliant. And looking at you I would never have thought you were severely obese as a child…

Amanda Salis: Well not as a child, I was a fat kid, but severely obese as a young adult, but now I’ve lost 30 kilograms and I’ve kept it off for a lot of years…more than 18 years in fact.

Chris Neff: That’s brilliant. You are looking at different diets and the way that people process food…so, you know when we think about all these things and we hear that protein’s good, carbs are bad, fat is are bad. How do you mediate between all the different kind of diets that we hear about?

Amanda Salis: So, the world is full of conflicting messages about nutrition and what is optimally good for human health and weight management, and wellbeing. So there are a lot of confusing messages out there about human nutrition.

And human nutrition is an area of research that is incredibly complex; food is made up of many components; macronutrients, micronutrients. Also health is a multi-dimensional thing as well, there are so many aspects to health, more than just weight or cardiovascular diseases, it’s the whole ‘shebang’…mental health, everything together!!

But there are some messages from nutrition research that are clear as crystal, and these are messages that have made their way in to the public health recommendations in countries all around the world. And these messages are reducing the amount of processed foods you eat. This is something that all health agencies agree on. Everyone agrees that having a variety of foods is important, and that’s because food contains things that are good for us; macronutrients and micronutrients and also things that are bad for us, like toxins or anti-nutrients that block the absorption of good nutrients.

So, by having a variety of foods you mix it up and get a variety of everything good and not too much of anything bad.

Chris Neff: What about the carbs question? Like, remember in the 80’s when everyone said stop eating butter and start eating margarine. So, my whole family stopped eating butter and started eating margarine and then 20 years later they were like, “it really doesn’t make a difference”. You know, I feel that way a little bit about carbs…I’m a carb-o-holic if that’s a thing. Are carbs the devil, or what should we do about carbs?

Amanda Salis: And I can see the nice big box of lollipops on your desk, so I can see you really are a carb man I think. 

Chris Neff: Oh yeah.

Amanda Salis: So the thing about carbs is, we need carbohydrates. Obviously fitting in with those public health guidelines about reducing processed foods, obviously the less processed carbohydrates are better. So, the healthy carbs are the ones we want, things like oats, brown rice and wholemeal pasta etc. Things with a lot of fibre and chewy things…these are good. The processed ones, we want less of those. And the carbohydrates are important because they contain a lot of nutrients, fibre, vitamins…they are important for our diet.

Chris Neff: So carbs won’t kill you?

Amanda Salis: Aaah carbs will actually make you live longer, they are a beneficial food.

Chris Neff: Then what are people on about?

Amanda Salis: Now the reason why this whole carb phobia has come about is that nutritional research has traditionally been done in a way that looks at one nutrient and one outcome. So this is in the days of scurvy…and it was discovered that for example “if you don’t have vitamin C you get scurvy, and if you put the vitamin C back you don’t get scurvy, or you cure the scurvy”.

In looking at complex diseases like diabetes, obesity, cardiovascular disease, it has been traditional to look at “ok, well let’s see what happens to cardiovascular disease risk if you remove carbs and put them back”, and it’s only taking a single nutrient view on the problem.  

Chris Neff: So I’m going to continue to eat carbs basically. So setting aside the moral reasoning around people who eat meat, or don’t eat meat; is there….nutritionally, is there anything better or worse that they need to be aware of?

Amanda Salis: The thing is, so around the world there are so many different diets, but there is not one single diet that we can say is better than any other diet. As long as those general principles of public health nutritional recommendations are followed, like variety; fruits and vegetables; reducing processed foods…we hear a lot about the Mediterranean diet. And that’s a diet which, again, is low in processed foods and high in fruits and vegetables and natural oils, it’s got a balance of a variety of different foods; some fish, some legumes, a bit of meat, not too much. So, that’s been proven to be beneficial in reducing cardiovascular disease risk. But it’s not the only diet that is helpful and beneficial.

I was in Norway a couple of weeks ago, meeting the author of the new Nordic diet. So it was a publication, a lovely clinical trial on testing the Norwegian style of food. And it’s based on what’s available, there’s fish and it’s salted oily fish, not a whole variety of fruits, but they’ve got some berries and it’s seasonal. And that has shown also to be very beneficial for health as well. So there’s no single style of eating that we can say is better than others, as long as it follows those general nutrition public health principles.

Chris Neff: I mean I used to joke for years/last week that most of what I eat comes in a box or through a window. And those are the problem items I’m guessing?

Amanda Salis: Well it depends how the food is processed. It’s not processed food per se, which is a problem…I mean we need food processing…we need it, because otherwise we can’t feed the whole world, we need to be realistic about it. But it’s the number of additives; it’s the amount of steps being taken to get that food from the farm into that box you are eating from. So, its really thinking in terms of how much has this food being manipulated….

Chris Neff: I don’t think my food has been manipulated at all [Amanda laughs]…

[music plays]

You are listening to Open for Discussion, a University of Sydney podcast that looks at research through a personal and critical lens. I am your host, Chris Neff and we are exploring the science of eating a healthy diet with my guest Amanda Salis.

Can we talk about the paleo diet a little bit, because there seems to be a lot of attention to it and it does seem to be one of those fads that has come about and people are swearing by the paleo diet. What are your thoughts about the paleo diet?

Amanda Salis: So there’s a lot of different interpretations of the paleo diet, and some research has shown that many people who follow a paleo diet are actually following, really closely, the public health recommendations for nutrition, which is a great thing. So they are actually eating small amounts of processed foods; treats, all that fun stuff, chocolate and things; minimum amount of processed foods; they’re eating large amounts of plant materials, so vegetables and in some instances fruit as well; a bit of meat, but also a variety of protein sources; some lentils, eggs…and this is really close to the public health recommendations and that’s a great thing.

Other people follow paleo and interpret it in a slightly different way; they’ll reduce carbohydrates to a great extent, so they’ll have less than 40grams of carbohydrates per day, where as you or the average adult might need around 150 or 200 grams of carbohydrates a day, so it’s very restricted in carbohydrates. And this has been shown in medical research to significantly reduce appetite. So a lot of people swear by this very low carbohydrate style of eating because they feel that “oh thank goodness, at last my appetite is under control…when I eat carbs I feel hungry, I just want to eat more”. I hear a lot of people talk about a sense of relief “it’s so much easier to manage my weight, I don’t feel hungry”.

But that’s only one aspect of health, there’s also your risk of disease later. And other research and it’s using a more broad framework, it’s called a ‘nutritional geometry framework’ that is being developed…lead by leading nutritional researchers here, at The University of Sydney. That’s showing that low carbohydrate, and high protein is beneficial for reducing fat, but it may not be as beneficial for other aspects, for example control of blood glucose and potential development of diabetes.

Chris Neff: Isn’t carbohydrates...ones of these things feeds the brain…isn’t carbs brains food? Like, I always say to my friends “stop going to the gym and be more interesting”. [Amanda laughs]. So, worry less about taking pictures of your food and just be a more interesting person…

Amanda Salis: Carbohydrates are a brain food, they are also a gut food. So, when you eat a low carbohydrate diet…well, in an extreme case a very low carbohydrate diet that is high in animal protein, there’s not much carbohydrate that gets in to the gut and down deep in to the intestine and the bugs that live in the intestine, they don’t have much to eat and so bad bugs can come in and take over.

Where as if you eat a diet that’s got carbohydrates and has got a lot of fibre, particularly, then that feeds the good bacteria in the gut and this has effects that influence the whole body for the good, and also affect the brain as well. So carbohydrates not only feed the brain directly, but there’s emerging research that the bugs in your intestine that eat the fibre from the carbohydrates that you eat, also produce products that have an influence on your brain and the whole of your body.

Chris Neff: Ok. Are we talking parasites (the little bugs) or what are we talking?

Amanda Salis: We are talking bacteria that live in your gut. There’s around ten times as many bacteria on your body and in your body as there are cells in your body, and these are very important.

Chris Neff: So we have to feed the bacteria. Well, my love of carbohydrates knows no bounds.

Ok, well…one of the things I saw was nine years ago, you published a book titled ‘The Don’t Go Hungry Diet’, which you say is about a lifestyle diet and not a calorie restriction diet.

Amanda Salis: I wrote this book based on the frustration of seeing many people around me who always struggled with hunger as they lost weight. And as I was struggling with hunger when I was severely obese, it never worked and eventually I would get hungry. So I wrote this book to show people that if you listen to your bodies hunger signal and eat accordingly, then you can actually manage your weight. Because our bodies are designed to be at an optimum weight and when you gain excess weight, your hunger levels will actually be reduced.

So what happens if you listen to those signals very closely, they are quite hard to hear as the signals are quite faint, especially when you’ve got windows that produce boxes of food that are easy to obtain; it’s hard to hear those signals that tell you if you’re not hungry or that you’ve had enough. But if you do tune into them and listen closely then you can regulate your weight because your body will do the regulating for you.

Chris Neff: What’s a…what is a hunger signal?

Amanda Salis: So you might feel a…some people feel it in the grumbling of the stomach, some people feel it in terms of feeling a bit weak or light headed, a mood change. My husband feels my hunger in me, he says “you’re hungry aren’t you”, which means I’ve probably snapped at him or something. So you can feel hunger in a whole lot of different ways but any feeling that can be reliably prevented or reversed by food is hunger.

Yeah, so the book is based on hunger and how you’re listening to your hunger and eating mostly healthy foods according to hunger [this] can actually lead to better weight management. And there’s a whole lot of different ways to losing weight and keeping it off, there is no one size fits all. In our research at the university here we are trying a whole range of different approaches to weight management, because different approaches work for different people. What didn’t work for me, and what doesn’t work for a lot of people is having to count foods. The instant I thought about that I just wanted to binge eat on copious quantities of food. And that’s where listening to hunger signals for me was incredibly liberating. Because instead of thinking ‘oh no I can’t eat because I’m only allowed, you know, 3000 kilojoules (or whatever) per day’. Instead of thinking that I just thought ‘yep I can eat what I want, when I want, I just have to wait until I’m hungry before I eat it’. And for me that was like…well that was a life change, it changed my whole life.

So, we are using that strategy in clinical trials for people with binge eating disorders or bulimia nervosa and we are using that approach of listening to your hunger signals instead as a way to manage weight.

Chris Neff: I love that. So can I ask, I remember when I was really short on money so I could afford two $1 double cheeseburger’s from McDonald’s, and that was it. So one went in the fridge and I had one for lunch and one for dinner. And I ballooned up, I definitely I gained weight. And then last week I remember there was this story about the ‘Oodles of Noodles’ the (instant noodle) food that a lot of our students eat; it’s got like 7 times as much sodium as a normal meal, you know, they end up with hardening of the arteries because they have ‘oodles of noodles’ everyday. But that’s because that’s what they can afford because it’s, you know, $1 for 5.

So where does socio-economic come in to nutrition? Because it is…it can be expensive. What should people from lower socio-economic background, or people who are advising them…what should we be telling people who don’t have the money to…?

Amanda Salis: I know that’s a really important issue. And the fact is that nutritional diseases based on excess of some nutrients and deficiencies of other nutrients are diseases that affect people of low-socio economic status. So this is a really important issue and something that my research doesn’t cover. But it is something that does need investigation and consideration.

What’s important to know is that eating well does take time and it does take money. But there are some options for people to consider, like for example; less processed foods are not necessarily more expensive than more processed foods. And in fact there’s research to back that up and it’s showing that eating a healthier diet is not necessarily more expensive than eating an unhealthy diet, but it does take time to prepare and finding those sources of food in markets etc. But, lentils and beans are generally a very good source of protein and nutrition.

When I was a student in Geneva, at the end of every month my scholarship would dry up so I would eat a lot of white bread and jam, because that’s all I could afford on my scholarship at the end of the month. But also a lot of lentils and cheap veggie based dishes and got through them all.

Chris Neff: A year ago you published a conversation on the science of ‘hangry’, or why some people get angry when they’re hungry. I understand it’s one of the most read articles of all time on the conversation, which everyone should subscribe to or follow on twitter. Tell us a little bit more about the science and why you’re more likely to have a shorter fuse when you are hungry?

Amanda Salis: So being angry and snappy is one of the signs of hunger, and that’s related to the fact that hunger is a stress response. So lack of food elicits a stress response, it’s survival. But what lack of food does, and it can do this even between meals is that it elicits a stress response in your body. So for example you will have cortisol; the stress hormone pouring out of your adrenal glands when you’re hungry and this has effects to increase your blood glucose level and help you feed the brain with glucose in the blood. This stress response from hunger will also increase the release of adrenaline from your adrenal glands and this is the fight or flight hormone; you know when you see something in the dark and you think ‘oh my goodness what is that’ and you can feel your body flooding with fright, that’s adrenaline, which can make you behave in all sorts of ways and at the same time your brain is responding to hunger with changes in neuro-chemicals that regulate hunger. But what we’ve shown, and other researchers have shown, is that these same chemicals in the brain that respond to hunger and drive us to forage and hunt for our food, these same chemicals are regulating mood, anger, aggression. So they are very closely linked. And it makes sense when you think in terms of hunter gathering and fighting for limited resources.

Chris Neff: Exactly, anybody who has a partner and has ever done a long car ride, knows that there’s a moment in the car ride where ok it’s time to pull over [Amanda laughs] because you need something definitely.

[music plays]

I think your research is really fascinating and I really appreciate you sharing it with us. Thank you for coming to Open for Discussion.

Amanda Salis: My pleasure.

Chris Neff: Thanks for listening to Open for Discussion, a University of Sydney podcast. If you have feedback about today’s episode, email us at Also if you’ve enjoyed this episode please review it on iTunes. 

Related podcasts