When people think of “sugar,” they usually think of the white stuff in candy or cookies — but sugar actually comes in many forms, and the human body treats them a little differently. Sugar is a type of carbohydrate — it’s your body’s way of getting energy. There are different types of sugar, and they’re found in all kinds of foods, not just sweets.
What Are the Simple Sugars?
All sugars your body uses for energy are built from three simple sugars: glucose, fructose, and galactose. These are called monosaccharides, and they’re the only sugars your body can absorb directly. More complex sugars — like sucrose, lactose, or maltose — are broken down in your gut into these basic units before being absorbed.
Breaking it Down
- Glucose – A “simple sugar” and this is the body’s favorite fuel.
— It can be found in small amounts in whole foods, but generally is made by breaking down other food. In its straight form, think of that glucose drink to test for diabetes during pregnancy. - Fructose – another “simple sugar” and the one found in fruits and honey.
— Sweet and natural in its raw form, but also found in added sources like high fructose corn syrup. - Sucrose – This is what’s in most candies, soda, and desserts.
— This is table sugar and is glucose + fructose stuck together - Lactose – the sugar in milk.
— Made of glucose + galactose stuck together. - Maltose – found in malted grains and some cereals.
— Made of two glucose molecules stuck together.
How the Body Handles Sugars
Even though glucose and fructose are both simple sugars, your body handles them differently:
- Glucose is absorbed directly into the bloodstream from the small intestine. It raises your blood sugar, triggers insulin release, and is used by nearly every cell in your body for energy. Some of it goes to the liver, but most is available for muscles, the brain, and other organs for fuel immediately.
- Fructose is also absorbed from the intestine, but it doesn’t raise blood sugar or trigger insulin directly. Instead, it goes straight to your liver, where it’s processed. The liver can turn it into glucose, lactate, or fat. Too much fructose (especially from added sugars) can overwork the liver and may contribute to fatty liver disease or insulin resistance.
- Some people wonder if sugar makes it harder for the liver to “detox” because of this liver processing. While fructose processing doesn’t block the liver’s function, too much added sugar — especially fructose — can increase the liver’s workload and contribute to fat buildup in the liver over time. Let me be clear though, fruit is not the enemy and the fiber and nutrients that come with whole fruit are good. High fructose corn syrup on the other hand…not great.
What About Other Sugars Like Sucrose or Lactose?
Other sugars — like sucrose (table sugar), lactose (milk sugar), and maltose (grain sugar) — are made of two simple sugars stuck together. Your body breaks them down in the gut into glucose, fructose, or galactose, which are then absorbed just like the individual sugars. So even if you eat a cookie, drink milk, or eat a piece of bread, your body is still ending up with the same simple building blocks: mostly glucose — which your cells (including cancer cells) can use.
Now with that out of the way, do cancer cells “survive” on glucose/sugar? Technically, yes they do. However, to untangle the sugar and cancer story, we have to take it all the way back to biochemistry and the Kreb’s cycle. Does anyone have nightmares yet? I do!
Nightmares aside, the real question is, what, if any, is the relationship of sugar and cancer? More importantly, can changes to diet help or hurt someone who is undergoing therapy for cancer?
Before we do a biochemistry refresher, let me first say, this is only going to address sugar and cancer if cancer has already developed. Science shows us that that obesity increases the risk for several adult type cancers and is a whole different topic.
How Cells Use Oxygen to Make Energy
Cellular metabolism is just a fancy way of naming how your cells (including cancer cells) turn food into energy so your body can do stuff (like exist, grow, repair, etc.)
Step 1: Food In → Glucose
When you eat food — like bread, fruit, pasta, candy, and treats — your body breaks it down into glucose if it is in another form of sugar, then the glucose goes into your blood and travels to your cells to give them energy as I mentioned above.
Step 2: Glucose → Energy
Normal cells use oxygen efficiently to make energy from glucose— like a car engine burning fuel cleanly.
- If oxygen is available, cells do something called aerobic respiration to break down that glucose to form energy.
- Aerobic respiration = (glycolysis → Krebs cycle → oxidative phosphorylation), and through this process the cell makes about 34 units of energy (called ATP) from each glucose molecule. This happens mostly in tiny cell parts called mitochondria (the “power plants” of the cell).
- However if oxygen is not available, like during intense exercise or in low-oxygen environments, cells switch to anaerobic (anaerobic = no oxygen) glycolysis.
- This skips the mitochondria, just breaks glucose into lactic acid, and only makes 2 units of ATP. It’s fast, but inefficient — like burning paper instead of coal.
| Pathway | ATP per glucose | Relative speed (ATP/time) | Oxygen required? | Key advantage |
|---|---|---|---|---|
| Glycolysis | ~2 ATP | Fast | ❌ No | Speed & precursor production |
| Oxidative phosphorylation | ~34 ATP | Slower | ✅ Yes | Efficiency |
What’s the Warburg Effect and Why Do We Care?
In the 1920s, a scientist named Otto Warburg noticed something odd: Some cancer cells often choose to use the less efficient method (glycolysis → lactic acid) even when oxygen is available. This is then called aerobic glycolysis (aerobic because oxygen is available) but the cells still don’t use the more efficient process. That’s weird, right? Why would a cell take the low-energy shortcut when it doesn’t have to?
Why Do Cancer Cells Take the Low Energy Shortcut Then?
- Oxidative phosphorylation is great at making ATP (lots of energy)… But it burns glucose all the way down, leaving little behind for building materials.
- Aerobic glycolysis is less efficient for energy, BUT it leaves half-digested pieces of glucose that can be re-routed into making DNA, proteins, and fats.
- So cancer cells “waste” glucose on purpose — not to be energy-efficient, but to support rapid cell division.
- It creates an acidic environment (from lactic acid), which may help cancer cells invade tissues and escape the immune system (I know many of you have question on this too, and I’ll try to address this in a later post).
It’s tempting to think that cutting carbs or going sugar free/keto would “starve” a tumor, since cancer cells love sugar. But it’s not that simple. Your brain and muscles need energy too. And cancer cells are crafty — they’ll find other fuels if they have to. So, while diet might support cancer treatment, it’s not a magic off-switch.
In larger trials with adults and cancer, ketogenic or low sugar diets haven’t consistently delivered strong results. But why???
1. Cancer cells are metabolically flexible
I often say cancer is stupid, but the reason it is stupid, is that I have to treat it and it’s actually very smart and cancer cells don’t just use glucose – they constantly adapt.
- Many tumors can switch fuel sources: glutamine, fatty acids, ketone bodies (ketones are backup energy sources made from using fat stores when glucose is low).
- Some cancers upregulate mitochondrial metabolism and thrive even when glucose is scarce.
- Others can import ketones and use them efficiently for energy — defeating the purpose of the diet.
In short, cancer cells basically reroute their metabolism in the face of low glucose.
2. Not all cancers rely on glycolysis
The Warburg effect is common — but not universal.
- But many tumors, especially low-grade or slow-growing ones, don’t show strong glycolytic activity.
- A one-size-fits-all dietary therapy doesn’t match the diversity of cancer biology.
3. The body maintains glucose levels anyway
The brain and red blood cells still need glucose, so your liver makes it.
- On a ketogenic diet, the liver ramps up gluconeogenesis, making glucose from amino acids and glycerol.
- So even with carb restriction, there’s still glucose in circulation — and cancer cells can grab it.
- Unless you’re actually starving (which is dangerous and unsustainable), you never truly “cut off” glucose.
- This is the most important take-away in my opinion. If there is no glucose in a human body, that human body is dead.
4. The tumor microenvironment complicates things
It’s not just the cancer cells — it’s their neighborhood.
- Cancer interacts with immune cells, stromal cells, blood vessels — all of which respond differently to metabolic changes.
- A ketogenic diet might temporarily impair immune function in some contexts (e.g., T cell activity), which could actually help the tumor.
- Some cancer-associated fibroblasts may supply nutrients to the tumor even under low-glucose conditions.
Bottom Line for Children with Cancer
Today, most children with cancer survive — and that changes how we think about supportive therapies, including nutrition. While ketogenic diets are being explored in cancer care, especially for adults, their role in pediatric oncology is unclear and could be potentially risky:
- We’re not just aiming for survival — we’re aiming for healthy survival. Kids need calories, protein, vitamins, and minerals not just to fuel treatment, but to grow, rebuild, and thrive long after therapy ends.
- Growth and development are especially important, even when children are being treated for cancer.
Strict ketogenic diets can impair growth by:- Lowering IGF-1 (Insulin like growth factor) and other growth-promoting hormones.
- Creating nutritional imbalances that can affect bone health, muscle mass, and cognitive development.
- There’s no strong evidence to date that ketogenic diets improve survival in children with cancer
Putting it all together from my perspective
Children with cancer do better when they are well-nourished, physically active, and emotionally supported. Nutritional therapies or should never compromise growth, healing, or quality of life.
It’s not that you can’t adjust your child’s diet during cancer therapy — you absolutely can, and in some cases, thoughtful changes can support how a child feels or functions during treatment. But it’s important to know: dietary change is not required to “fight” cancer. There is no single food that cures it, and no single food that causes it. If changes to nutrition help your child feel better, reduce side effects, or give you a sense of control — that’s valid and worth exploring with your care team. But if all your child can manage is toast and apple juice some days, that’s okay too. Remember, the goal is nourishment, not perfection.
Got Questions? I can try to answer them the best I can, drop them below!
Thanks for the valuable information to spread truth.