Is Sugar Really Bad For You? with Dr. Rehka Kumar

An endocrinologist helps answer that question and explain the effects of sugar on our health.

Sugar. It’s blamed for everything from cardiovascular disease to obesity to hyperactivity. But what is the truth behind sugar? NewYork-Presbyterian and Weill Cornell Medicine endocrinologist Dr. Rekha Kumar breaks down how sugar impacts our health, walks us through the differences between natural sugars and added sugars, and also unpacks why artificial sweeteners may not be a healthier option.

Episode Transcript

Faith: Welcome to Health Matters. Your weekly dose of the latest in health and wellness from NewYork-Presbyterian. I’m Faith Salie.

Sugar. It’s blamed for everything from cardiovascular disease to obesity to hyperactivity. But what is the truth behind sugar? 

As we’re all navigating holiday treats and sweets, we invited back NewYork-Presbyterian and Weill Cornell Medicine endocrinologist Dr. Rekha Kumar to break down how sugar impacts our health. She walks us through the differences between natural sugars and added sugars. She also unpacks artificial sweeteners, and why they may not be a healthier option. 


Faith: Welcome back to the show, Dr. Kumar. We’re so happy to have you.

Dr. Kumar: So excited to be back.

Faith: So, we’re here today to talk about sugar. Let me start with this question. Is sugar really that bad for us?

Dr. Kumar: Fundamentally, sugar is not so bad for us at all when consumed in the appropriate quantities found in nature. We have made sugar bad because of the way that we process it, manufacture it in mass quantity, and now consume it in mass quantity. It’s something that never was inherently bad. 

It is the most fundamental source of energy for humans. Our bodies use sugar to convert calories into energy and to allow all of our organs and cells to function. When consumed in excess, we get a lot of extra calories, we can gain weight easily, develop diabetes, increased inflammation, increased risk of heart disease. So it’s really in excess that sugar increases the risk of many chronic diseases.

Faith: What is going on in our body when we consume sugar?

Dr. Kumar: So what is supposed to happen when we consume sugar is that we eat something that either has simple sugar or more complex carbohydrates that are then absorbed by the gut, broken down into simple sugar, and that’s what goes into our cells to create ATP or energy. In excess, what happens is, in addition to just getting extra calories, the liver gets overloaded.

The role of the liver here, once the sugar is absorbed, table sugar or sucrose is made up of glucose and fructose. Fructose is a simple sugar that can’t be used by our body. It needs to be turned into glucose. So fructose in our food, drinks or whatever it is, needs to go through the liver and be turned into a form of sugar that’s usable, which is glucose.

When we get too much table sugar or high fructose corn syrup, that fructose overwhelms the liver and is stored as fat, and that’s what we call fatty liver, and that increases the risk of diabetes, heart disease, chronic inflammation, and various cancers. 

Faith: Is there a difference between natural sugars, like the sugar in fruit, and added sugars, like the sugar in candy? Is one healthier than the other?

Dr. Kumar: So, sugar in fruit. We’ll talk about that first. So that is fructose, actually. Which is also – it’s confusing because people say fructose is so bad, high fructose corn syrup is bad. Fructose in fruit does occur in nature. It’s just meant to be consumed in such small quantities. So if you’re eating berries, melon, banana – something that occurs naturally – there is fructose there. It does go through the liver, is turned into glucose, and then used. 

The problem with added sugar or added fructose in the form of added sugar or high fructose corn syrup is that there’s so much more fructose than ever found in nature. And that’s the part that overwhelms our liver.

So it’s something that the human body and the human liver isn’t used to handling or has not evolved to handle because it does not occur in nature in that quantity.

Faith: Does the body know to differentiate between receiving a whole bunch of table sugar or a banana?

Dr. Kumar: No, technically the body doesn’t know. It just knows where to send it, and so if all the fructose is supposed to go to the liver first and the difference is between eating a banana which the fructose gets shunted to the liver, either stored as glycogen back up carbohydrate storage or turned into glucose and then goes into cells to make energy. 

But say you had a Coke and so it’s probably several times the amount of fructose than in that banana. It’s still the same process. It just still sends all the fructose to the liver, but it’s overwhelming to the liver.

Faith: Right. And it also – a Coke doesn’t come with potassium and fiber and, and all the good stuff that fruit comes with, right?

Dr. Kumar: Absolutely. And that’s the definition of empty calories.

Faith: What are common sources of added sugar in our modern diet?

Dr. Kumar: Really common sources of added sugar would be things like sodas, fruit juice, and then in quotes “fruit juice” or “fruit drinks” and energy drinks.

Faith: How do they impact our health? What does it do to us when we down a whole soda or an energy drink?

Dr. Kumar: In the short period we feel like we have energy, we feel like we could be more productive, but what’s actually happening inside of our body is our blood sugar is going up. The hormone insulin is going up and we make more insulin in order to use the energy or the carbohydrates. 

When you’re constantly living at a high insulin level, so say you are drinking multiple sodas a day, eating multiple baked good products, then you’re living at a higher insulin level. Eventually, your body doesn’t respond to insulin as well, and that’s called insulin resistance, and that is like the underlying cause of many diseases, including type 2 diabetes, polycystic ovarian syndrome, various forms of inflammation, cardiovascular disease.

When we overwhelm our bodies with too much added sugar, too much fructose, too much high fructose corn syrup, we become insulin resistant. And if you have a genetic tendency towards that, meaning people in your family have type 2 diabetes, or you gain weight easily, those people need to be extra careful.

But I’d say nobody’s really protected because it is just becoming so prevalent to overwhelm our systems with added sugar.

Faith: Sugar comes in lots of forms, right? I mean, you mentioned table sugar. We hear honey is better than sugar, you know, if you’re giving something to a kid, and, and corn syrup’s the worst, and then I feel like agave had a moment.

From a doctor’s point of view, is there a meaningful difference among all those sugars?

Dr. Kumar: No, there is not a meaningful difference from a health perspective of table sugar or sucrose, honey, agave, molasses, all those things that occur in nature or people seem to think that they are healthier because they’re natural. It’s still sugar, it’s still calories, and it still puts the same stress on the body.

Faith: Okay, you said the word natural, which leads me to the word “artificial.” 

So, I am so curious about artificial sweeteners. They have been in the headlines. In the simplest terms, where do artificial sweeteners come from? A lab?

Dr. Kumar: So they could come from a lab and be completely a manufactured chemical that tastes sweet, often much sweeter than regular sugar. Another way that artificial sweeteners can be created in a lab is by tweaking regular sugar. So an example would be a sugar alcohol like sorbitol or xylitol. We see it on, like, packs of gum or baked goods that are supposed to be low in sugar.

So that’s tweaking the sugar molecule to turn it into a sugar alcohol, which is more difficult to digest. So although that doesn’t spike your blood sugar, it’s a sweetener, but also could cause digestive problems. 

Faith: What’s the difference with the way our body processes them from the natural sugars?

Dr. Kumar: The reason that artificial sweeteners are so prevalent is that they were thought to really not do anything. Many have no calories. They’re extremely sweet. Another word for them is non-nutritive sweetener. So they didn’t do anything. They didn’t provide nutrition. They didn’t give you calories. They just created a sweet taste.

The recent news about them is: are they actually harmful and could they cause DNA damage and increase the risk of cancer? There was always little side conversations of this dating back to the 1970s. 

There was a thought that one of the artificial sweeteners caused bladder cancer in rodents, but that didn’t prove to be true in humans, so we went on another 40 years to increase our consumption of these things. But what we’ve learned is that likely high consumption of artificial sweeteners alters our taste profile, leads people to crave sweeter things, because many sweeteners can be 600 times as sweet as table sugar.

So your taste profile changes, and natural foods don’t taste as good to you anymore.

Faith: How dangerous are these for our bodies? There are headlines from the World Health Organization that link artificial sweeteners to diabetes and death.

Dr. Kumar: Yeah, it’s somewhat ironic because these sweeteners were created hopefully to avoid obesity, avoid diabetes and heart disease, or at least to mitigate the risk, but now we’re saying the opposite, that these non-nutritive sweeteners, low-calorie sweeteners are actually increasing the risk of these exact diseases that they were supposed to prevent. 

And likely what’s happening is that consuming these in high quantities are changing a taste profile, leading people to consume other unhealthy highly processed foods then undoing any benefit one could have gotten from using an artificial sweetener as a replacement. It was supposed to be used in small quantities to add sweetness to something, but when they’re in everything and people are consuming larger quantities of these foods, it’s leading us to an increased risk of diabetes and metabolic disease.

Faith: I mean, when you hear DNA damage from regular consumption of this stuff, it sounds scary. Is that reversible? If you stop consuming things that cause DNA damage?

Dr. Kumar: DNA damage, really, we don’t know how to reverse it all the time. In certain scenarios, you could treat a tumor with targeted therapy, but that’s not how we want to approach this problem.

We really need to look at prevention because we can’t allow on a population level people to consume these things, increase the risk of cancer and, you know, think we could just treat that. We would definitely prefer prevention.

Faith: Any other practical tips on making informed decisions about sugars and sweeteners? You know, for example, a lot of people have an afternoon slump and they want to reach for something sweet just to get them to dinner time or get them home from the office.

Dr. Kumar: Yeah, so a way that I ask my patients to not overthink this is to just fill up on lean protein and vegetables. So, for example, if you have that slump at three o’clock, eating an apple with peanut butter or almond butter or fruit with cheese, you want to balance whatever sugar you’re getting in with fat and protein to stabilize the spike in blood sugar, which then will stabilize the spike in insulin.

Faith: It’s the holiday season, and sugar is all around us, right? And stuff we have nostalgia for and look forward to all year. We got the sugar cookies, and the candy canes. 

It sounds like you’re very compassionate in seeing your patients as human. So what advice do you offer to navigate the holiday season when we all want to indulge?

Dr. Kumar: My advice would be to try to maintain some semblance of their non-holiday season routine. I think there’s also this, “well, now it’s the holidays, like, it’s all falling apart.” It doesn’t have to if you maintain some semblance of routine otherwise. 

So, besides for the parties, eat your healthy meals. Maintain your exercise routine when you’re not traveling. You’ll actually make it through the holiday season just fine. You’ll enjoy the parties. You’ll be able to consume things that you see as treats or holiday food without it impacting your health in a negative way.

Faith: Dr. Kumar, thank you for explaining all this to us. It was a pretty sweet conversation.

Dr. Kumar: Of course, it’s a fun conversation.


Faith: Our many thanks again to Dr. Rekha Kumar.

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