Written by
Louise W Lu, PhD, MPH, BMLS
Written/Reviewed by
Alexandra V Goldberg, Registered Dietitian
Recently, two high-profile journal studies have pushed the “cooking oil” debate into the spotlight.
One study, published in Nature Metabolism by the Harvard team, revealed:
Animal fats (lard, beef tallow, butter) impair immunity and accelerate tumor growth, while plant oils such as olive oil and coconut oil did not show this effect.
Does this mean olive oil is always safer?
Not necessarily. Another study, just published in Cancer Research, reminds us:
A high-fat diet based on olive oil may actually promote lung metastasis of triple-negative breast cancer!
So why do different oils lead to such different results?
Animal fats, olive oil, and MCT—
how should we choose?
And how much oil is safe to eat each day?
This article will break it down for you.
These two latest studies were published in Nature Metabolism and Cancer Research.
Animal Fats vs Plant Oils: Different Impacts on Immunity and Tumors
A Harvard University team published in Nature Metabolism used an obese mouse model. The researchers fed the mice two types of high-fat diets:
- Diet based mainly on animal fats (lard, beef tallow, butter)
- Diet based mainly on plant oils (olive oil, coconut oil, palm oil)
Both groups of mice became obese. The researchers then implanted tumor cells into these mice to observe immune function and tumor progression.
In the animal fat diet group, the mice’s immunity declined significantly. Anti-tumor immune cells (such as T cells) showed reduced infiltration and impaired function, and tumors grew faster.
👉 Put simply, the body’s “anti-cancer soldiers” were weakened: they couldn’t reach the battlefield or fight effectively, giving tumors the chance to expand.
In the plant oil diet group, although the mice also became obese, immune function remained normal, and tumor growth was not further accelerated.
👉 In other words, the “anti-cancer army” could still fight as usual: obesity was present as a risk factor, but it did not cause the immune system to give up, nor did it allow tumors to speed up.
Practical Significance
This study shows that different fat sources have completely different effects on immunity and tumor progression:
- Long-term high animal fat intake: weakens immunity and promotes tumor growth.
- Plant oil diets: relatively “neutral” in terms of immunity and primary tumor growth.
However, this does not mean olive oil or coconut oil can be consumed without limits. Later studies have found risks such as promoting metastasis. At least on the level of immunity, the harm from animal fats is greater and more direct.
The “Dark Side” of Olive Oil: Possible Promotion of Cancer Metastasis
In the previous section we saw that animal fats impair immunity and speed up tumor growth, while plant oils seemed relatively “safer” in this regard. But is olive oil truly risk-free?
A study published in Cancer Research gave a new answer. The research team found:
- When mice were fed a high-fat diet based on olive oil, their immune function was not weakened, and tumor growth did not accelerate;
- But these mice showed a striking change: lung metastasis of triple-negative breast cancer significantly increased.
What counts as a “high-fat diet”?
In scientific research, “high-fat” has a clear definition:
- Normal diet: Fat provides about 20%–30% of total daily calories.
- High-fat diet: Fat provides more than 40% of daily calories; some experiments even use 45%.
👉 To put this in perspective: if someone eats 2000 kcal per day, and 800 kcal comes from fat (≈90 g of fat), that already qualifies as a “high-fat diet.”
Why does this happen?
The study further revealed the mechanism: the main fatty acid in olive oil is oleic acid. With the help of Fatty Acid Binding Protein 5 (FABP5), oleic acid integrates into cancer cell membranes, then activates the PKC/ALDH pathway, giving cancer cells greater “stemness” and “mobility.”
👉 Put simply, cancer cells use oleic acid to “arm” themselves — they escape faster from the original site and can settle down in the lungs.
Research Findings
In animal experiments, the olive oil diet group of mice developed:
- More lung metastatic nodules
- Higher expression of metastasis marker ALDH
- Larger areas of metastatic tumors
This indicates: although olive oil does not promote tumor growth, it may worsen disease progression by another route — promoting cancer metastasis.
Note: this applies under “high-fat diet” conditions, not normal everyday small amounts of olive oil use.
Real-World Reminder
This does not negate the cardiovascular benefits of olive oil, but it does remind us:
- Even “healthy oils” should not be consumed in excess
- For high-risk groups — especially patients with triple-negative breast cancer or those with a family history — olive oil intake should be approached with extra caution
MCT Oil: Comparison and Advantages
From the previous findings we know:
- Animal fats can weaken immunity and promote tumor growth;
- Olive oil, while relatively “neutral” for immunity, may promote cancer metastasis under high-fat diet conditions.
So, what is a relatively safer type of fat?
Let’s take a closer look at MCT oil (Medium-Chain Triglycerides).
The Fundamental Difference Between MCT Oil and Olive Oil
Olive oil is mainly composed of long-chain monounsaturated fatty acid — oleic acid (C18:1). Research has shown that oleic acid, with the help of Fatty Acid Binding Protein 5 (FABP5), can integrate into cancer cell membranes and activate the PKC/ALDH pathway, which makes cancer cells more capable of spreading and metastasizing.
👉 Layman’s note: Oleic acid is like giving cancer cells a suit of “armor” — it helps them resist attacks and run faster.
MCT oil is primarily composed of medium-chain saturated fatty acids (C8 caprylic acid, C10 capric acid). Their metabolism is entirely different: they go directly to the liver and are quickly converted into ketones for energy, rather than embedding in cell membranes.
👉 Layman’s note: MCT oil acts like “quick-burning fuel” — rapidly consumed by the body without equipping cancer cells with extra armor.
👉 In other words, MCT oil does not have the same risk mechanism as olive oil, and in studies it did not show increased lung metastasis nodules, higher ALDH expression, or expanded metastatic areas.
Comparison Summary
| Type of Fat | Immune Effect | Tumor Growth | Metastasis Risk | Metabolic Feature | Suggested Daily Intake |
|---|---|---|---|---|---|
|
Animal fats (lard, beef tallow, butter) |
Weaken immunity, T-cell decline 👉 Anti-cancer troops are weakened |
Promote tumor growth 👉 Tumors grow faster |
No specific pathway identified, but overall higher risk 👉 A double hit |
Long-chain saturated fats, easily stored 👉 Eat more = gain fat |
Minimize, ideally under 10g/day |
|
Olive oil (rich in oleic acid) |
Immunity remains normal 👉 Anti-cancer troops keep fighting |
Does not speed up tumor growth 👉 Tumor stays on baseline growth |
Promotes metastasis under high-fat diet 👉 Cancer cells “learn to escape” |
Long-chain monounsaturated fat 👉 A slow-burning energy source |
Generally 20–30ml/day |
|
MCT oil (C8, C10) |
No adverse effects observed 👉 Doesn’t hold immunity back |
Does not promote tumor growth 👉 Tumor not fueled further |
No oleic acid, so no activation of metastasis pathways 👉 Cancer cells don’t get a chance to “escape” |
Quickly converted into ketones 👉 Clean, fast-burning fuel |
10–40ml/day, ideally split into doses |
Key takeaway: MCT oil contains no oleic acid, so it does not trigger the FABP5–PKC/ALDH mechanism seen with olive oil. This is why it is considered safer regarding cancer progression.
Real-World Meaning
In daily diets, MCT oil may be a safer option:
- Unlike animal fats, it doesn’t weaken immunity;
- Unlike olive oil, it carries no metastasis risk in high-fat diets;
- It provides quick energy and supports weight management and metabolic health.
👉 Layman’s note: If fats were fuels, animal fats would be “dirty coal,” olive oil “clean gasoline that may give hitchhikes to bad actors,” while MCT oil is like “clear quick-burning alcohol” — ignites fast, burns clean, leaves little trouble behind.
Want to explore or purchase MCT oil? Check here 👉 LOLU MCT Product Collection
