LEPTIN: THE BODY'S FUEL GAUGE
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Episode 263:
Show Notes
In this week’s episode of Real Health and Weight Loss, Dr Mary Barson and Dr Lucy Burns dive into the science of leptin — the hormone that acts as your body’s fuel gauge — and how it connects to obesity, hunger, metabolism, and more.
This is Part 2 of our series on obesity, where we continue busting myths and exploring the real drivers behind weight gain.
- Obesity is complex – It’s shaped by genetics, environment, behavior, lifestyle, childhood experiences, and social factors. There’s no one-size-fits-all solution.
- Leptin’s role – Produced by fat cells, leptin regulates appetite, metabolism, and energy. It tells the brain about fat stores, helping control hunger and energy use.
- Leptin resistance – Common in obesity. High leptin levels are present, but the brain doesn’t respond properly, resulting in ongoing hunger, reduced motivation, and a slower metabolism.
- More than weight – Leptin also affects mood, inflammation, fertility, sleep, and joint health. Chronically high levels can drive low-grade inflammation and increase the risk of heart disease, autoimmune conditions, neurodegenerative disorders, and osteoarthritis.
- Lifestyle matters – Poor sleep, stress, late-night eating, and disrupted circadian rhythms worsen leptin resistance.
- Support leptin sensitivity by:
- Eating whole, protein-rich foods for better satiety
- Avoiding ultra-processed foods
- Trying intermittent or time-restricted eating (especially earlier in the day)
- Moving your body regularly, even a little
- Managing stress and prioritising good sleep habits
- Portion control isn’t enough – For people with leptin resistance, hunger can overpower willpower. Long-term success needs more than just eating less.
- Medications can help – GLP-1 medications support some individuals, but aren’t substitutes for lifestyle changes. They should be used with care, aiming for the lowest effective dose and avoiding rapid weight loss.
- No shame, no blame – Obesity isn’t about willpower, and using medication doesn’t mean failure. Sustainable success often comes from a mix of “pills and skills.”
- Small steps add up – Tiny daily habits, like walking 5 minutes, can make a big difference over time.
Episode 263:
Transcript
Dr Mary Barson (0:04) Hello, my lovely friends. I am Dr Mary Barson.
Dr Lucy Burns (0:09) And I'm Dr Lucy Burns. We are doctors and weight management and metabolic health experts.
Both (0:12) And this is the Real Health and Weight Loss podcast!
Dr Lucy Burns (0:21) Hello, my lovely friend. How are you this morning on this beautiful Tuesday morning, which is the time that the podcast actually comes out — but maybe you're listening to it on a Friday afternoon, who knows? But wherever you are, and whenever you are, I hope you are having a wonderful day. And of course — well, I say "of course," it's not "of course" — quite often I'm joined by other people other than the fabulous Dr Mary, but today I am joined by my partner in crime, the wonderful, spectacular Dr Mary. Hello, lovely. How are you?
Dr Mary Barson (00:51) I'm good, I'm good, I'm feeling — I'm feeling good.
We just had our Momentum retreat on the weekend, and I feel fabulous after spending a weekend connecting with these amazing women in our Momentum program. So yeah, I feel good.
Dr Lucy Burns (01:09) Oh, I know, I know — it was a spectacular retreat, and I think, you know, you can't underestimate the power of, you know, in-real-life connection. I mean, online connection is good, but it doesn't — it's not a substitute for, you know, human-to-human touching connection. So yeah, you're right, it was amazing, and, you know, I think we can probably do a podcast particularly around the things that we did on that retreat, which was really largely around how to manage stress and how to manage your emotions and your emotional health and all of that — because it plays such a huge role in being able to do the things that improve your lifestyle, the things that you know you probably should do but you haven't implemented.
Dr Mary Barson (01:54) Yes.
Dr Lucy Burns (01:55) But anyway, today we're talking — we're doing part two of our series on obesity and, basically, you know, myth-busting some of the — again, my thing that rattles my cage is the influencers who just say to people, you know, you just need to eat big bowls of jelly and it's all about volume, low calorie, you know, whatever you need to do, just, you know, eat as much food — the size of your food is the thing that matters. And whilst stretch receptors in your tummy, in your stomach, do have a role, it is tiny, that role. Otherwise, none of us — we would all just be able to fill up on cups of tea and never get hungry.
Dr Mary Barson (02:31): That's right. It is really important to understand that it's a complex — it's a complex issue for which we need to tackle it in multiple ways all at once. And so, last week we talked about all of the multiple causes of obesity and how it's such a complex interplay between your genetics, your environment, your behavior, your lifestyle, your childhood, and your, you know, your social environment. Today we're going to dive in a little bit more into one of the biggest players, which is leptin. Leptin is extremely important, and the reason that leptin is so important is that lots of people who have obesity — people living with obesity — have got high levels of leptin and deranged leptin signaling. And this is really important because we've mentioned this before: that people with obesity are not metabolically the same as thin people or as people who do not carry extra weight. It's physiologically and metabolically different, and so the treatment for obesity is different to the prevention. And, you know, you were mentioning this before, Lucy — if you are someone who's in a smaller body and only has a little bit of weight to lose, the strategies that might be effective for you are not necessarily going to be effective for someone who has a lot of weight that they want to lose.
Dr Lucy Burns (04:03): Yeah, absolutely — and this is what, you know, again, grinds my gears: that people provide these solutions and go, "This is all you need to do," and, you know, the context for that is, "So if you can't do it, then that's on you," when in fact I look at that and go, "Well, actually, that advice is wrong." So today we're going to talk a whole heap about leptin. So we've spent, you know, over the years we've spoken a lot about insulin — insulin being our fat storage hormone, insulin being the hormone that locks away fat stores so you don't have the energy, you know, easy access to your energy. You know, insulin locks away the woodshed, as we've spoken about. But another big, big player in this whole picture is leptin. And I mean, the irony being, right — when I went through medical school, leptin hadn't been discovered. Like, we didn't even know it existed.
Dr Mary Barson (04:56): Yeah, a lot of this stuff is new.
Dr Lucy Burns (04:57): Yeah, whenever we discover something new, you know, we have to have lots of research on it — and an example being that they discovered that people without leptin — so there are, unfortunately, a few people born in the world with genetic absence of leptin.
Dr Mary Barson (05:15): Very rare. Very rare.
Dr Lucy Burns (05:17): Yeah, it's really rare — but those people develop severe obesity from a very, very young age, and basically they have zero off switch. They literally never, ever, ever have that feeling of fullness — ever. So they can consume huge amounts of food and never, ever feel full. Like, it's almost like it's torture, really, isn't it? It's like being — it's like having an unquenchable thirst — so, insatiable hunger. So they go, "All right, okay, well clearly here leptin's the key." So we just need to give people more leptin, and that will stop their hunger and they will lose weight and we'll have cured obesity — which, you know, which sounds reasonable, doesn't it? I mean, it's...
Dr Mary Barson (06:03): Did that work, Dr. Lucy?
Dr Lucy Burns (06:05): Yes. Spoiler alert — no. No, no, it didn't work at all. It worked — it did nothing. Nothing. In fact, if anything, it actually made it worse. And you're thinking, you know, Julia Sumner Miller style, "Why is this so? How could this be?" You know, you've got a hormone that is supposed to tell your brain that it's full, that's supposed to regulate your appetite — and if you've got none, we know what happens. But if you've got more, well then, why is it not working? You know — enter stage left — the concept of leptin resistance. So today we're going to unpack all of these things. So, Miss, I thought maybe you could start just by explaining to our beautiful friends listening today: what is leptin? Like, what exactly is it?
Dr Mary Barson (06:51): Leptin — it's a hormone made by our fat cells, and it plays this key role in regulating our appetite, our metabolism, and our body weight. You can kind of think of leptin as your body's fuel gauge. It tells our bodies, you know, how much stored energy — fat — we have, and whether or not we need to eat more or eat less. When everything's working well — when leptin levels are nice and stable, and the leptin signalling is working well — then it's a great way for us to help sort of maintain our weight. So it's — how does it work? It's made by our fat cells, our white adipose tissue, and then it travels through our bloodstream and into our brain, crosses the blood–brain barrier into our brain, and then acts on a part of our brain in our hypothalamus, which controls the hunger and our energy expenditure. So when leptin levels are high, it sends a signal to your brain that says, "Hey, we're good on energy. We're good right now — no need to eat anymore — we're feeling full, beautiful." And it even sends some signals to your brain: "Go burn some energy instead — here's some energy — go out, be motivated, move." And that's great. But when leptin levels — when leptin signalling — falls low, then the message is, "Oh, we're low on reserves. We need to eat more. We have to conserve energy. We've got to do this now." So that's a basic overview of how leptin signalling works. Essentially, it turns off hunger-promoting signals when it is turned on, and activates satiety signals so that we feel full and we feel ready to go out and attack the world. But that's when it's working well.
Dr Lucy Burns (08:35): Yeah. And it's part of, you know, just to add the sort of third little leg into that stool, is the metabolic rate. And for those of us — those out there who have listened to us for a while — we love talking about your metabolic rate. Your metabolic rate is the rate at which you burn fuel just particularly lying around doing nothing. I mean, how awesome is that? You know, you can lie in your hammock, and you're burning fuel. And, you know, two people can be lying in the same — well, maybe not the same exact hammock — but in similar hammocks. And one will be burning fuel at a different rate to the other. And yeah, leptin has a role in that as well, along with — as we've talked about — along with muscle mass, along with oestrogen, along with a whole host of hormones. So it is — it's a very, very important hormone. But it's got, like lots of things — these little hormones, they get up, they get like these side gigs, don't they? They get like an extra job. It's not enough just to have one job. I've got to have a whole host.
Dr Mary Barson (09:30): No, they have lots of different jobs. So leptin doesn't just — it's not just involved in metabolism and in weight management and metabolic rate. It also plays a role in mood regulation, and it plays a role in cartilage regulation, in fertility and inflammation, heart health — lots of things — which is great when things are good, but is terrible when things are bad.
Dr Lucy Burns (10:01): So, Miss, we know when, you know, when the body is working well — when everything is in balance — then it works beautifully. We have, you know, energy going in, energy going out. We can access our fuel stores. We're motivated. We've got all the things that are going really well. Good metabolic rate. What happens, though, when things start to go awry? What are the other things that leptin does, apart from, you know, being involved just in our hunger, satiety, and metabolic health?
Dr Mary Barson (10:29): Yeah, because high leptin levels — it's not just a weight loss problem. So chronically high leptin levels affect multiple systems in our bodies, many of which can be quite harmful to our health. So one of the biggest ones is chronic inflammation. Leptin itself acts very similar to pro-inflammatory signals in the body. It's really similar — structurally similar — to inflammatory signals called cytokines. And it has a similar effect. And high leptin levels — especially when it's prolonged high leptin levels, which happens with people with obesity — it promotes low-grade chronic inflammation throughout the body and the brain. And this is linked with all kinds of illnesses like heart disease, like autoimmune illnesses, neuroinflammatory disorders, neurodegeneration, and can really adversely affect our life expectancy and our health span. It's also — it's an independent risk factor for heart disease just in and of itself. High leptin is an increased risk factor. It definitely has a strong association with high insulin. So leptin and insulin — they dance sort of lockstep together. And when you've got elevated insulin, you often have elevated leptin, and vice versa. So there's that strong association with all of the issues with high insulin — happens when you've got high leptin. But it also affects mood as well. So leptin affects our brain, including areas of our brain that are important for emotion, memory, and reward. And high leptin has been linked to depression and anxiety — and anxiety and those neuroinflammatory, neurodegenerative disorders that I talked about before, including Alzheimer's disease. And also it affects our reproduction. So leptin regulates certain hormones that are involved in our fertility — particularly female fertility — luteinising hormone, follicle-stimulating hormone. And high leptin can cause PCOS-like symptoms with irregular periods and infertility. Poor sleep as well — leptin normally sort of rises later at night. So all these hormones have their own little natural rhythms. But when leptin signalling is off — because of high leptin and associated leptin resistance — then this interferes with our melatonin and our cortisol balance, and it can worsen people's sleep. And also, it affects our joints, and it affects the cartilage in our joints and can promote osteoarthritis. So — lots of things.
Dr Lucy Burns (13:14): Yeah, absolutely. And I think on that osteoarthritis — I know a lot of people think that it's just caused by the mechanics, you know, the weight going through the knee or the weight going through the foot or the hip or whatever it is. But it's way more complicated than that. And leptin — sneaky little thing that it does — small amounts of leptin, it is the ultimate Goldilocks hormone, because small amounts are good. They help the chondrocytes, which are the fancy name for cartilage cells — they stimulate the chondrocytes. So that's nice. But then, once we tip over into that bit where we've got too much leptin, it actually turns off chondrogenesis. So it turns off making cartilage and turns on osteogenesis. So it turns on bone formation within the cartilage, which is why people with osteoarthritis often get, like, bony spurs. They've got little bony peaks in there if you look at knee X-rays. And that's nothing to do with the weight going through — that's the leptin. So really, again, it's understanding that we don't need to be stick thin to be healthy by any stretch. As you all know, we are banging on all the time about being a hottie. But there are, unfortunately, consequences that affect multiple organs when our body is storing more fat than it was designed to do.
And it's really therefore about helping people do everything they can to reduce that body fat — without doing it in a shaming or starving or unhelpful, you know, mean-girl way.
Dr Mary Barson (14:57): Yes, that's right. Apart from anything else, that ain't going to work. It's not helpful. And you don't need to be a stick figure to be healthy. You don't need to be a fitness model to be healthy. But carrying a lot of extra weight is detrimental to our health. And there are lots of things that you can do — ways in which you can nurture yourself back to health with love and with kindness — when you've got the right information and the right advice.
Dr Lucy Burns (15:22): Yes, absolutely. And I really like the, you know, the understanding that, again, when people have leptin resistance, it is a bit harder. I'm not going to say it's a walk in the park. You know, we often will talk about the idea that we like to try and make weight loss easy. And there are certainly easier ways to do things. And, you know, it's a combination of the right food with the right macronutrients. There are foods that are more satiating than other foods. And, you know, people have heard me, I think, many times talk about the Tim Tams versus the boiled eggs. And for those of you who perhaps haven't heard this little story, I'll give you the 30-second rendition, which is that, calorie for calorie, nine Tim Tams has the same calories as 12 boiled eggs. And, you know, the old me — and probably the old you, Miss — could sort of polish off nine Tim Tams pretty easily. And, in fact, because there's 11 in the pack, probably just finish off the last two for good measure. I can solemnly swear that I have never put back a packet of Tim Tams that's got two left. So — and that's not that hard to do. Like, honestly, you just sit there, you know, maybe over an hour watching telly, dipping it into your tea. It was pretty easy. Twelve boiled eggs — like, honestly, there is no way, come hell or high water, that I could eat 12 boiled eggs over an hour. I would just — you know, I can even now think about it, as I'm, you know, I've had my fourth or something. I'd get to the fifth, and you just get that little bit of — because you're full. You're full. Boiled eggs — they're protein and fat. They have very low dopamine activity. So it is easy for our brain, therefore, not to mix up hunger with desire. And so it's a really, really good experiment to do. Not that I'm suggesting you go out and buy a packet of Tim Tams to wolf that down, but just a really good comparison. And ideally —
Dr Mary Barson (17:29): so it's a thought experiment.
Dr Lucy Burns (17:30): Yeah, a thought experiment. And it just indicates, though, that we are wanting to work with our bodies, because our bodies do have signalling that will tell you that you're full — but that it can get usurped by particularly ultra-processed foods. And so we do know that people with high leptin maybe find it a little harder to eat smaller portions, which is why when people talk about "portion control, portion control" — I don't know what you think about portion control, Miss, but I found portion control excruciating.
Dr Mary Barson (18:04): And I think that, long term, it doesn't win. I mean, we can decide what we eat, and we can decide when we eat. But in the long run, our bodies will decide how much we eat. Hunger generally wins in the long term. We can put up with being hungry for a while, but it's not a long-term solution. And so we can take steps to heal our leptin resistance and repair our leptin signaling and reduce our leptin by focusing on those things that we can control — which is the what we eat. And you already mentioned, you know, eggs are going to be more satiating than the entire packet of chocolate Tim Tams. So focusing on whole foods — those non-processed whole foods — really prioritising your protein, that is going to help regulate our hunger. So that's the what that we eat, but also when we eat. And there are studies showing that some intermittent fasting, or just giving yourself a break from food — times when you don't eat — especially when it's combined with a real food diet and also combined with some movement, helps lower insulin and improve insulin signaling. And movement too — movement is something that also helps improve our leptin signaling.
Dr Lucy Burns (19:18): Yeah. Sorry, Miss, you mentioned that intermittent fasting lowers insulin signaling. Does it also lower leptin signaling?
Dr Mary Barson (19:27): It lowers leptin. Sorry, sorry. It lowers leptin signaling.Yeah, it lowers leptin signaling.
Dr Lucy Burns (19:31): And I'm imagining that there's — and again, I don't have this study at the tip of my fingers, you may, Mears, being the science buff — but I'm imagining that eating, it is probably better for leptin if we eat earlier in the day and certainly don't eat in the evening.
Dr Mary Barson (00:47): Yeah, that is to do with our circadian rhythms. So leptin — and the leptin hormone — is influenced by and influences our melatonin signaling and our cortisol signaling. So we do need to talk about stress, because high cortisol also impacts leptin signaling — and high stress. High cortisol can be a contributor to leptin resistance, as can poor sleep — can be a contributor to leptin resistance. Sleep disruption, stress — these things also impair leptin signaling. And not eating big meals at night helps with our circadian signaling, helps with our sleep, and therefore also has flow-on effects to our leptin signaling. And doing anything that we can to promote our sleep and our natural circadian rhythms is going to be really helpful for our leptin signaling — like avoiding blue lights at night, having a regular bedtime — whenever that is, if you're a night owl or a morning lark — just a regular bedtime, prioritising your time in bed so that, you know, you really can give yourself the best opportunity to get a good eight hours’ sleep. Ideally, if you can. You know, you can't get eight hours’ sleep if you only spend five hours in bed — it's just, that's impossible. And yeah, that's right. Morning sunlight is also helpful for our circadian rhythms and our circadian cycles. But yes, stress also — so stress impacts our leptin signaling. So taking steps to reduce your stress as much as you can is also going to be helpful. So we've got what we eat, we've got when we eat, we've got how we sleep. We manage our stress, moving our bodies — all of these things are going to help improve the actual biochemical signaling within our body that is driving obesity, driving inflammation, driving chronic health problems. And we have the power. And the beautiful thing is you don't need to be perfect — but you do need to start. And once you start, you need to keep going. And you can — you absolutely can.
Dr Lucy Burns (21:57): Yeah, absolutely. And I guess one of the things I would say in that — so, you know, we mentioned earlier that leptin, when leptin is working well, we have sort of motivation to move. We've got good energy levels when leptin is high. So when we've got hyperleptinemia, that actually slows down our metabolic rate, slows down our desire to move, slows down the satiety. So we do kind of end up, you know, eating more and moving less. And so, whilst it's never, as you know, about maths — calories in, calories out — what we also know is that sometimes, if you're waiting to feel like moving, and if you have high leptin, well, that feeling may not come. So we spend a lot of time talking with our people about, you know, cognitive behavioral therapy, which is really about, you know — thoughts control your feelings, control your actions. Actions can go back to feelings. Actions can influence your thoughts. So the little triad there — or, as Dr. J recently called it, think, feel, do. So if you're waiting for motivation, waiting to feel like moving your body, well, that feeling may not come while your leptin is high. So sometimes we actually just have to do. And the thought can be — again, your thought might be, "Well, I don't feel like it, so therefore I'm not going to do it." Or the thought could be, "Well, I know I'm not going to feel like it until my leptin is sorted, so I'm just going to have to do it anyway." And when we do, then we go and we do it and we go, "Oh, well, it actually wasn't as bad as I thought it would be." That then starts this little cycle of, you know, momentum — what a great word that is — because you've done it a bit. And again, you don't need to go out and run a marathon or you don't need to hike bloody Kilimanjaro. You just need to go, "Well, I'm just going to walk to the end of the driveway today and that'll do." And that's fine. You know, you might do that a few times. And then the next day, even though you don't feel like it, you've already put on your shoes because you've already talked yourself into the fact that you're only doing, you know, 200 metres down to the end of your driveway. And then you think, "Well, maybe I'll just go down the end of the street." And stuff begets stuff.
Dr Mary Barson (24:17): Yep. Action begets action. And small actions compound quickly. So you don't need to go out there and change every aspect of your lifestyle right now. Small actions are powerful, and we need to embrace them and not be afraid of them. Your brain may want to reject the idea that a small action is helpful because, you know, "I've got so much I need to change — why on earth would walking to the letterbox every day help?" But the truth is, it really does. And the only way to get there is one small step at a time. And before you know it, you've scurried all the way up and achieved your goals one little step at a time.
Dr Lucy Burns (24:54): Absolutely. Isn't there some famous philosopher that says that the longest journey starts with the first step? Correct. Yes, yes. Indeed. And then the first step makes the second step, makes the third step. I guess I want to do a little just, you know, before we finish up — we're about to finish this lovely podcast — is, you know, again, we've spoken a bit about it, the weight loss medications, injectable weight loss meds. They do have a role for people, okay? Not everybody needs them. They do have a role, though. And I feel like that role — that role — it needs to be managed by somebody who really has a good understanding of metabolic health, of all of the factors at play, because you will have people tell you that the reason these medications work is because they stop your hunger. It's more complex than that. And the management and titration of them often requires somebody who's sort of skilled in it, who's had some experience. Because at the end of the day, what we want for everybody is to be able to have the lowest effective dose. And I see — I've seen people, it's terrible, terrible for them — because they've been put onto doses that are super high. They've lost weight incredibly quickly. They've lost lots of muscle mass. They've run out of money because they're expensive. And particularly if you're using big doses. And rather than promoting this sort of just beautiful kind of rebalancing — to use one of our favorite words — of their metabolic hormones, they've basically just driven a truck through their metabolism, and they've ended up in a worse place than when they started. So, by all accounts, I think if GLP-1s or injectable weight loss medications is something you're considering — do so. But make sure you see somebody who is experienced in them, because it's not just write a script, see you later.
Dr Mary Barson (26:46): Yep. And someone who can give you that ongoing support and help you troubleshoot your way through it. Yeah, GLP-1s work on a totally different mechanism to leptin resistance. So they're similar, but related. But all of these things to help improve your leptin resistance need to happen as well as the GLP-1s.
Dr Lucy Burns (27:04): Yes, it's pills and skills.
Dr Mary Barson (27:08): Pills and skills. I love it.
Dr Lucy Burns (27:10): Yeah, absolutely. You don't need to be ashamed of needing medication. That is not a — it's nothing that, you know, people always feel guilty or like they're taking the easy way out. There is no shame in that. It's not a one-trick pony. What we do is use these so that you can do all of these other things that will help long-term and restore your beautiful health. Good.
Dr Mary Barson (27:31): That's our little tour through leptin and leptin resistance, beautiful people. It's complex. It's a big topic. And there are many, many, many things you can do to rebalance your beautiful body back to great health.
Dr Lucy Burns (27:48): Absolutely. All right, lovely friends. We will see you next week with part three of our series. I can't remember what we called it — something like, you know, myth-busting
Dr Mary Barson (27:59): Myth-busting obesity
Dr Lucy Burns (28:00): busting through. Take good care of yourselves. Have a fantastic week.
Dr Mary Barson (28:04): See ya.
Dr Lucy Burns (28:07) The information shared on the Real Health and Weight Loss Podcast, including show notes and links, provides general information only. It is not a substitute, nor is it intended to provide individualised medical advice, diagnosis or treatment, nor can it be construed as such. Please consult your doctor for any medical concerns.
