Am I Destined To Be This Size?
We all know that person—the person who can eat whatever they want, never care about exercising, and yet… they’re always in shape. But, is there actually a genetic component to weight? Or is there just some behaviors we’re not seeing them do? How much of our weight do we control? On this week’s episode, we interview Dr. Ruth Loos, Dr. Brad Lowell, and Dr. Dana Small to get to the bottom of weight and genetics.
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Guests
Dr. Ruth Loos is an epidemiologist and the Director of the Genetics of Obesity and Related Metabolic Traits Program in the Charles R. Bronfman Institute of Personalized Medicine.
Dr. Brad Lowell is a Professor of Medicine at Beth Israel Deaconess Medical Center & Harvard Medical School. His research is focused on how neural circuits generate hunger cues and how “hunger” impacts behavior and physiology.
Dr. Dana Small is a Professor of Psychiatry at Yale School of Medicine. A current focus of her research is the impact of diet on gut-brain signaling, perception, and cognition.
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Juna: So if you're listening to this, you've probably had the thought, once or a thousand times, that
there just seemed to be certain people in your life who basically eat whatever they want and also
just never gain weight. Eddie, I suspect that you may be one of these people, first of all. But
second of all, have you ever encountered any of these types of people?
Eddie: First of all, I deny the charges. I'm not one of those people. I am concerned about what I eat
because if I eat the wrong things, I will and do gain weight. But I know the people you're talking
about. I've seen them. They eat whatever they want, and it can drive you nuts.
Juna: You're over here busting your butt, eating really healthy, exercising, sleeping well, reducing
stress, all the things you're supposed to be doing and nothing is happening. Oh, and then there are
other people who are like eating whatever they want, sit on the couch all day and they're just
skinny mini little things. And I'm like, maybe I'm just destined to be big-boned. Maybe it's just
genetic.
Eddie: I love that phrase, "I'm just big-boned."
Juna: Maybe I'm just destined to be this way forever.
Eddie: So this is a great thing to talk about in this episode of Food, We Need To Talk. I'm Dr. Eddie
Phillips.
Juna: And I'm Juna Gjata. To get to the bottom of this, I found an expert on genetics and weight.
Ruth Loos: Ruth Loos, L-O-O-S. And I'm a professor in environmental medicine and public health at
the Icahn School of Medicine at Mount Sinai.
Juna: I asked her the burning question, how much of our weight comes from our genetics?
Ruth Loos: I would say it's about 50/50. So what that means is that of all the variation you see in a
population in weight, 50 percent of that variation is due to the fact that these people differ
genetically.
Juna: Wait so Eddie, where it is the other 50 percent of the variation in weight come from?
Eddie: So Juna, that would come from the environment or more specifically, the toxic food
environment that surrounds us and the kind of environment that you create within your home.
Are you bringing in those hyper palatable foods, the junk foods, to surround yourself with? And
the rest of it is actually going to be other behaviors like how much you're exercising, how much
are you eating?
Ruth Loos: We have evolved from times that there was no food. Only the people who were able to
store fat easily, they would survive. Whereas, the people who were not able to do that, they
would die.
Eddie: So, Juna, no matter how much we hate it, it actually makes a lot of sense that our genes are
there to help us gain and keep weight.
Juna: Oh, thanks, Eddie. That's very reassuring now that I can't fit into a size four like I wanted to.
Eddie: Well, Juna, hearing all of this from Ruth Loos, what do you think?
Juna: I was a little confused as to why there are all of a sudden is an obesity epidemic now, as
opposed to the past like millions of years?
Ruth Loos: That's a good question. So definitely our genome itself hasn't changed in thousands of
years. The epidemic has happened over the past 40 years. So you'd say, OK, it's the changing
environment that is the cause of the epidemic. But it's still a combination of both genes and
environment in the sense that it's the individuals who are genetically the most susceptible, who
will respond the most to the changing environments. A smart person a 100 years ago once said,
like, it's the genes that load the gun and the environment that pulls the trigger.
Eddie: So to understand how the environment pulls the trigger, so to speak, I think we first need
to understand how our body actually regulates our weight and our hunger.
Juna: Yeah. And as with everything human biology related, it's very complicated. So we definitely
need another expert. This is Dr. Brad Lowell, who is a professor at Harvard Medical School and a
researcher.
Brad Lowell: You know, during the process when you're eating a meal, when you get full, there's
mechanisms inside your intestines release hormones to then decrease your appetite so that you'll
stop a meal. But after you've completed a meal and you haven't eaten for a while, eventually the
energy stores and your body will get lower and then they will cause you to want to eat again.
Juna: For example, Eddie, one of the main systems we know that regulates our body weight, is a
little hormone called leptin. Have you ever heard of it?
Eddie: Yes, leptin. So it's this hormone. It's actually released by your fat cells. So if you have very
little fat, like you're starving or you've been fasting,
Juna: Can't relate.
Eddie: You have low levels of leptin. So this signals your body that you need to go find and eat
food. But if you're very overweight or you have large fat stores, you have very high leptin, and this
should tell your body that you don't need food.
Juna: Not so fast, though. Dr. Lowell says if you're looking at mechanisms like leptin, it's really
important to look at what levels of leptin it actually has an effect.
Brad Lowell: The high levels of leptin don't work to prevent obesity.
Juna: It turns out, leptin works at low levels, so it works to tell you to get food.
Eddie: Yeah.
Juna: It works at normal levels, which just tells you to stay the same weight. But it doesn't work at
high levels.
Brad Lowell: So yes, we have definite mechanisms that would cause you to terminate a meal. And
they work well. But the thing is, there's many systems to get you to eat and not so many to stop
you from eating.
Eddie: So, Juna, our bodies have these hormone mechanisms like leptin that encourage us to find
food and eat until we're full. But those same mechanisms are in competition with lots of other
stimuli when it comes to ending the meal. We just tend to keep on eating even when we're full.
That kind of sucks, right?
Juna: And we haven't even gotten to the agouti-related peptide yet.
Eddie: The what?
Juna: Here's the important part, there is these neurons deep in the hypothalamus of your brain
that Dr. Brad Lowell has found,
Brad Lowell: And they are sensing the energy state of the body. So when you don't eat for a while,
they become very active.
Juna: In his experiments in genetically modified mice, he can basically turn these neurons on and
off whenever he wants with a button. And what he finds is that when he turns them on,
Brad Lowell: Even in a mouse that's already Thanksgiving dinner, has no reason to eat anymore
and won't eat anymore, if we force these neurons on, it'll have another Thanksgiving dinner.
Eddie: That sounds like,
Juna: It sounds like a problem.
Eddie: Well, it can easily lead to excess weight, right?
Juna: Yes.
Eddie: But none of us has actually been genetically modified. So I'm wondering, why does this
really matter?
Juna: OK, well, Dr. Brad Lowell may not be turning our neurons on and off, but maybe someone or
something else is.
Brad Lowell: Think about our environment that we have with all of these signs, billboards,
commercials, this and that. And you think, this sensory cortical process information can get down
to these body weight sensing neurons. And then you realize that our environment can affect how
hungry we are.
Eddie: Oh, that's so evil.
Juna: Right? So this might lead you to the question, is there something fundamentally different in
the brains of those who are susceptible to weight gain as opposed to those who aren't?
Eddie: And what's the answer?
Juna: You're just going to have to wait till we come back from a short break.
Eddie: OK.
Juna: OK, Eddie, we've learned that genes make it more likely for some of us to gain weight, but
now we want to know, is there something different in the brains of the people with that genetic
predisposition?
Eddie: This is psychologist and neuroscientist,
Dana Small: Dana Small, and I'm a professor of psychiatry at Yale University School of Medicine.
Juna: She was trying to see if there was a difference in the brains of those who are overweight
versus those who weren't. And basically, this involved a lot of adolescents and college students
drinking some very tasty, high-calorie milkshakes in the lab.
Eddie: Coffee flavor?
Juna: Per chance.
Eddie: OK.
Juna: And having their brains scanned while they were doing so. And basically, she was trying to
see, is there a correlation between activity and any certain brain region to their body mass index,
or their BMI, which is a measure of your height and weight ratio?
Dana Small: We were sort of expecting, you know, to see the midbrain, which is where all the
dopamine neurons are. And sometimes it's referred to as the pleasure center. We were expecting
that that area would be higher in people that had higher BMI.
Eddie: So, Juna, I get it. The people who like the food more are going to derive more pleasure from
it, right? They're going to show this big fireworks in their pleasure center. And that would probably
put them more at risk for eating more and more and getting more and more overweight.
Juna: Yeah. So they did find that, which makes sense because that's been found in study after
study, after study. But they also found something new and much more interesting, which is a
lower response in a different brain region called the striatum.
Eddie: The striatum.
Juna: And this brain region is involved in impulsivity.
Dana Small: So in this area, the response to the milkshake was actually inversely related to BMI.
So the higher the BMI, the lower the response.
Juna: So the striatum is involved in impulsivity. That's why a lower response in the striatum,.
Eddie: Makes you,
Juna + Eddie: More impulsive.
Because you can't regulate your impulses as well, right?
Dana Small: The lower the response, the higher the scores people made on tests of impulsivity.
People that score high on questions of impulsivity are more likely to be overweight.
Eddie: So, what I'm wondering is, which comes first. Does the predisposition to be impulsive make
you eat more and worse food? Or is it actually eating the food and gaining the weight that changes
your brain?
Dana Small: I think both of those things happen. If you are born being more impulsive than
somebody else, you may indeed be at greater risk for overeating. But I also think that if you eat a
high fat diet, there is evidence in humans and animals that parts of the brain adapt that are
important for regulating things like impulsivity.
Eddie: So that's really important because it seems like our actions as much or more than our genes
are actually what is changing our brain. Think about it. We're changing our brain, and then we
become even more susceptible to overeating. So let's hear again from Ruth Loos, who says that an
even better predictor of becoming overweight or obese as an adult is actually your family history.
Ruth Loos: Having one obese parents increases a child's risk to become an obese adult two-fold
compared to a child that has no parents that are obese. And having two obese parents increases a
child's risk by sometimes even 10-fold compared to someone who does not have any obese
parents. Family history is an important predictor, and parents pass on their genes, but they also
pass on their lifestyle.
Eddie: Wow. There is a lot going on here. Think about all the things we're hearing from our
experts. First of all, there are a lot of stimuli competing with the body systems to regulate weight.
On top of that, you can have genes that increase the likelihood of obesity. But even more than
that, you can inherit the lifestyle habits from your family that, on their own, or in concert with
your genes, contribute to weight gain. And this fuels changes in your brain that science is
suggesting can come with extra weight. It is a vicious cycle.
Juna: It's really easy to listen to all the stuff we've been talking about and just think, what the
heck? I'm screwed. There is no point in trying anything. I'm not going to try to eat well. I'm not
going to exercise because I'm basically just fighting my body on everything.
Eddie: Oh, Juna, let me show you the bright side of this one. You could also hear the same
information and say, this is somewhat liberating because actually our behaviors are within our
control. And you know what behavior can significantly lower the effect that you're predisposing
genes have on your weight.
Juna: What?
Eddie: My favorite topic.
Juna + Eddie: Exercise!
Ruth Loos: I think it's good news, right? It's not 100 percent genetic. And we've shown in studies
that even though some people have a high genetic susceptibility, if they are physically active, they
can suppress that genetic susceptibility by 30, up to 40 percent. So that's good news. It means that
it may be hard to lose weight or to resist weight gain, but it's possible.
Juna: And even beyond exercise, there are some really simple steps that have been shown in
studies, so they're evidence-based, to really change your eating behaviors in the long term.
Eddie: Here's Dana Small again.
Dana Small: We are at the point where we were able to cobble together a list of hints. And some
of them just make a lot of sense like eat slowly. Eat unprocessed foods. Don't eat unless you're
hungry. Don't keep snacks and cues around.
Eddie: So those cues that send you reaching for a snack, and are maybe easy to change, would be
getting rid of that bowl of candy on your desk or the kitchen counter. This is a kind of change
that's a low-hanging fruit. Come to think of it. Why not just reach for that low-hanging fruit?
Sounds simple, huh?
Juna: Yeah. I mean, I feel like I do a lot of these things, and there's obviously still aspects of my
weight that are definitely out of my control, unfortunately. I think that's kind of the point of this
episode is that, obviously your genes are loading the gun,
Eddie: But it's the environment that pulls the trigger. So maybe let's try to change our immediate
environment. Many of the decision points about what to eat begin in the supermarket. Make a
shopping list and begin to resist putting junk food into your shopping cart. I'll tell you, the part that
I heard that just blew me away was that by eating that processed, that high-fat food, that our
brains are actually changed. And that's then kind of make us more impulsive and then less able to
control our food choices. That is just horrifying.
Juna: I mean, that was like a little twilight zone.
Eddie: But maybe let's focus on the things that we do have control over.
Juna: Which are?
Eddie: Well, what's my favorite one?
Juna: Exercise!
Juna: All right. So as we talked about in our last episode, there's more reasons to exercise than just
burning calories. It actually can reduce those effects that the predisposing genes have on your
weight. So if that's not a reason to exercise, then I don't know what is.
Eddie: You can escape your genetic destiny.
Juna: Almost.
Eddie: A little bit.
Eddie: So, Juna, as you've done at the end of every interview, you asked Ruth Loos, what's the one
thing that people can change to most improve their health? And I'm going to guess that she said
exercise.
Juna: No, it's not exercise. It's not nutrition. Do you know what it is?
Eddie: What is it?
Ruth Loos: People need to take more time for themselves. I think particularly in the U.S., there's a
big drive for people to perform and to pursue that American dream, I think. But there's very little
time for themselves and also for their friends and all that.
Eddie: So, Juna, maybe we should cover stress.
Speaker 1: [00:16:22]Stress eating typically tends to be cookies and cakes and that kind of stuff, as
opposed to not a lot of stress eating of, say, celery and salad. [8.0s]
Juna: Sounds like a good topic to dive into because let me tell you, I am not an unstressed
individual.
Eddie: All right, Juna, just relax while I thank our guests, Ruth Loos, Dr. Bradford Lowell, and Dana
Small. If you're enjoying Food, We Need To Talk Please go to Apple Podcasts or wherever you get
your podcasts and leave a review.
Juna: Do it.
Eddie: It will help us reach more listeners.
Juna: Also, don't forget to follow us on Instagram @FoodWeNeedToTalk food. It's litty-lit-lit.
Eddie's giving tips. We're doing crazy stuff. We're making fools of ourselves, it's insane.
Eddie: And it's got wonderful content.
Juna: Yeah.
Eddie: But if you're listening to us and you have this burning question, send a voice memo to
foodweneedtotalk@gmail.com and we'll try to answer it in future episodes.
Juna: Food, We Need To Talk is a production of WBUR.
Eddie: Our editor and producer is George Hicks. This episode was mixed by [00:17:24]Paul Callow.
[0.3s]
Juna: Our supervising editor is Elisabeth Harrison, and our executive producer is Carrie Goldberg.
Eddie: With additional editorial and technical guidance from Catherine Brewer, Paul
[00:17:33]Vicous, [0.0s] and the WBUR iLab. I'm Dr. Eddie Phillips.
Juna: And I'm Juna Gjata, and I am going to go online shopping for some jeans now.
Eddie: Thrifty jeans, see what I did there?
Juna: No, thrifty jeans are in because skinny jeans are out.
Eddie: Oh.
