Hypothalamus size linked to obesity

The hypothalamus – the region that sits on the underside of the brain – as well as controlling things like sleep, body temperature, blood pressure and how thirsty we feel, also plays a key role in hunger. And researchers have discovered that it's noticeably larger in people who are overweight. Stephanie Brown from the Department of Psychiatry at Cambridge University conducted the research…

Stephanie - This study was focused on looking at brain structure in the context of body mass index. So as you mentioned, we know that a large number of factors influence how we eat and the types of food we eat, including genetics and hormone regulation and our environment. But we also know that this region called the hypothalamus sits at the base of the brain. It's about the size of an almond, and it plays a really important role in telling us when we're hungry and when we're full. So what we actually found is that when we did a large number of brain scans, the volume of the hypothalamus was significantly larger in people who were overweight and people who were living with obesity. And what we also saw is this significant relationship between volume of the hypothalamus and body mass index. And going down to further detail, these volume differences were really most apparent in the smaller regions of the hypothalamus that control appetite through the release of hormones to balance hunger and fullness.

克里斯,我们知道这是原因或结果? People have done studies on other parts of the brain, the London taxi driver study most famously where if you look at London taxi drivers who have to learn all of the streets of London, you find that one region of the brain concern with navigation, the hippocampus, is much larger in those taxi drivers and we think that it gets larger because it's the sort of use it and lose it phenomenon. So do you think it's that overeating enlarges your hypothalamus or do you think an enlarged hypothalamus causes you to overeat? Which way do you think the equation runs?

Stephanie - Yeah, so this is really the really important next question. In this research, we need to understand whether this change in the structure of the hypothalamus is a cause or a consequence. The reason we are thinking it might be a consequence is that in animal studies we see a high fat diet can cause inflammation of the hypothalamus, which in turn prompts insulin resistance and obesity. And this can actually happen really quickly. So in just three days of a high fat diet, we see this localised inflammation in animal models. So if what we see in mice is the case in humans, then a high fat diet could trigger localised inflammation of our appetite control centre. And over time, this would potentially change our ability to tell when we've eaten enough and then how our body processes blood sugar leading us to put on more weight.

Chris - Why would the inflammation occur and why would inflammation cause a change in how we process calories and how we choose to eat more of them?

Stephanie - Yeah, so that's a very good question. The answer is quite complicated because there's a lot of factors involved. But as a first step, we know that when we eat a high fat diet that can cause inflammation in the body, things like c-reactive protein, for example. And when these inflammatory processes happen, this can infiltrate the brain. And then what we know from this process in animal models is that the brain's localised immune cells, these are called glia, can increase in size. So what we think we are seeing is a reflection of this inflammatory process at a localised level in the hypothalamus.

Chris - While we've got you, Stephanie, can I ask you about one other paper I spotted this week in the Journal of Clinical Nutrition where researchers said that they reckoned that eating a handful of nuts every day was associated with about a 17% drop in your risk of depression. What do you make of that?

Stephanie - I think we always have to be really careful when we look at studies to not over-interpret the information that's being presented. So we know there's also a lot of lifestyle factors that can come into this as well. But from a biological point of view, it could be plausible. And that's because we know that nuts have anti-inflammatory properties and we know that inflammation in the body, whether this be through inflammatory disease stress or even obesity these things can be a risk factor for depression via this inflammatory process. So if we take this evidence together, it is possible that nuts might be a protective food to eat against depression because they may counteract inflammatory processes. But really much more research would be needed in that area to be able to draw any conclusions about that.