How Glucose and Added Sugar Relate to Testosterone and Reward Signaling
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In this clip from Dr. Rhonda Patrick's appearance on Modern Wisdom, she explains how added sugar can affect hormones as well as appetite. The study she cites did not test a dessert, sugary drink, or habitual added-sugar intake: 74 men completed a standard 75-gram oral glucose tolerance test, after which mean testosterone fell about 25% and remained below baseline at two hours. This was an acute response to a glucose challenge, not evidence that one sugary meal causes lasting testosterone suppression; the authors' clinical conclusion was that a low nonfasting testosterone result should be repeated while fasting. [1]
Dr. Patrick then discusses reward signaling. In a small human imaging study, higher habitual added-sugar intake was associated with greater dorsal-striatal responses to food cues after a glucose drink and a smaller GLP-1 response. The study was cross-sectional and included 22 lean adults, so it cannot show that sugar caused the brain response, reduced dopamine-receptor density, or produced an addiction. Animal studies support stronger mechanistic claims, but they should not be used to equate sugar with cocaine, methamphetamine, or nicotine in humans. [2]
Her practical focus is the pattern, not one isolated dessert. Ultra-processed foods combine added sugar with textures and flavors designed for rapid consumption, while whole fruit packages sugar with water, fiber, and a slower rate of eating. Reducing routine sweetened drinks and highly refined snacks can lower repeated glucose exposure and make appetite cues easier to recognize.
This clip is excerpted, with permission, from Dr. Rhonda Patrick's appearance on Modern Wisdom. Thank you to Modern Wisdom for allowing us to share it.
- ^ Caronia LM; Dwyer AA; Hayden D; Amati F; Pitteloud N; Hayes FJ (2013). Abrupt decrease in serum testosterone levels after an oral glucose load in men: implications for screening for hypogonadism. Clin Endocrinol (Oxf) 78, 2.
- ^ Dorton, Hilary M.; Luo, Shan; Monterosso, John; Page, Kathleen A. (2018). Influences Of Dietary Added Sugar Consumption On Striatal Food-Cue Reactivity And Postprandial GLP-1 Response Frontiers In Psychiatry 8, .
Chris Williamson: When it comes to the ultra-processed foods, what's in them, how they affect us outside of the palatability and the calorie density, what else is going on that seems to be evidence-based that's something that we should be concerned about?
Dr. Rhonda Patrick: Yeah, well, I think that part of it is that people are consuming more of it because they're not satiated, right? It's disrupting the hormones, which I mentioned. So that is the one thing to consider.
Chris Williamson: Is that the biggest mover in all of this?
Dr. Rhonda Patrick: For weight gain, I would say it is because like weight gain really is comes down to like eating more calories.
Chris Williamson: Calories out.
Dr. Rhonda Patrick: Right. Calories in, calories out makes a big difference. But, there's other factors at play here that I think really come down to the added sugar, right?
So, added sugar affects so many different things in the body, everything from hormone production to cognition. So, hormones, testosterone, I know you're interested in testosterone. There was a pretty classic study that was done that showed that men, and this was a huge age range, and we're talking young men that were like 17 all the way up to older adults. So, young adults, middle-aged adults, older adults, if they consumed 75 grams of added sugar, so that would be like a medium-sized donut and the Coke.
Chris Williamson: Okay. Not out of the— people do that all the time. 75 grams sounds like so much, but when you put it in terms of
Dr. Rhonda Patrick: A donut and a Coke. That's it. Yeah. It's not right.
Chris Williamson: There's, there's a lot of Americans eating a standard American diet and eating donuts with Coke or donuts with coffee and a bunch of added sugar in their coffee.
Dr. Rhonda Patrick: Right. So, it, it actually is something that I would say is pretty practical in terms of what people are consuming. And we, we can actually talk about what people are consuming in terms of added sugar, but 75 grams of added sugar. And this caused a 25% decrease in their circulating testosterone within a two-hour range. So, it's obviously transient, but nonetheless, 25% less, that's significant.
Chris Williamson: If you're chipping away at that grazing throughout the day.
Dr. Rhonda Patrick: Yeah, exactly. And imagine if people are eating, I mean, if their whole diet is nothing but ultra-processed foods, right?
So, you're talking, in that study with Kevin Hall, they actually calculated how much it costs to have the whole foods diet versus the ultra-processed food diet, and it was $45 more a week for the ultra— sorry, the whole foods diet. So that's significant. It adds up over like a month, right? So we're talking about $180 a month. It's expensive to be healthy.
Chris Williamson: For a lot of people, that makes a difference. And so it's like economically, people are economically incentivized to eat ultra-processed foods because they're cheaper. There's also— this is Calley Means's whole thing and Vani Hari's as well. About whatever the food stamp system is called.
Dr. Rhonda Patrick: Oh, right. SNAP?
Chris Williamson: Yes, SNAP.
The sorts of foods that tend to be available on SNAP, trying to eat in a more healthy manner on that is very difficult, more difficult. So what you mentioned there about what are Americans eating typically, what are they putting in their bodies? I mean, it's ultra-processed foods.
Dr. Rhonda Patrick: So, the refined sugar, or I'm calling it refined sugar, it's really added sugar also, it's kind of interchangeably, but ultimately people are eating 13% of their daily caloric intake is coming from added sugar. That's a lot. If you, a 2,000-calorie day, if you just consider that like on average, that's a lot of coming from sugar. In fact, guidelines, so the guidelines for like the strictest guidelines suggest no more than 5% of your total daily caloric intake coming from added sugar.
So, that would be no more than 25 grams a day, 5%. People are eating 13% of their total calorie intake from added sugar. So, added sugar is also affecting— probably what's happening also is there's a mechanism there. It's hyperpalatable. It tastes good. People want things that taste good, but there's an addictive— aspect there as well. And that's, that's been shown in certainly a lot of animal studies, but also some human data as well. So there's been studies showing that if, if people eat added sugar, it activates dopamine reward pathways in the brain, in the striatum, more than like eating fat, for example. So there was a study that compared fat versus added sugar. And so it's activating these dopamine reward pathways.
Animal studies have found that it's activating dopamine reward pathways much like addictive drugs do, but to a much milder degree, of course. So, what I'm saying is that you can have addictive drugs like cocaine, methamphetamine, nicotine will activate these dopamine reward pathways in parts of the brain. Sugar activates them too, to a much milder degree, of course. But, you know, in animal studies, they'll keep going back for the sugar like this addictive thing, right?
Chris Williamson: Yep.
Dr. Rhonda Patrick: Now, again, you got to take the animal studies with a grain of salt because we are not rodents. But, there is human evidence that these pathways are being activated in our brain with added sugar.
And, there's also evidence that if you look at people that are obese, the obesogenic diet largely consists of a lot of added sugar. Well, people that are obese have a lower density of dopamine 2 receptors, D2 receptors, really indicative of something called tolerance. So, what happens if you keep activating the dopamine reward pathway is that your body as an adaptive response, a feedback to it goes, well—
Chris Williamson: Habituates.
Dr. Rhonda Patrick: I don't need so many dopamine receptors because I got a lot of that signal coming in, right? But what ends up happening is when you have fewer of those receptors, then the little bit of dopamine that you have, you're not feeling it as much. It's you need more and more, right? And so, you know, you kind of connect the dots here.
And I would say certainly we need more evidence in the human arena on the, you know, potential addictive properties of added sugar. However, what we do have is a lot of animal evidence and, you know, some human evidence. And I think it really indicates that there is— it's affecting reward pathways, it's affecting our dopamine system, and that's, you know, unhealthy.
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