Saturated, monounsaturated and polyunsaturated fats: what science really tells us.
In one of my recent videos, I talked about a particularly interesting area of research: experiments in mice suggesting that the type of fat consumed in the diet may influence the development and progression of skin tumors.
I invited you to comment “OIL” if you wanted to explore the original studies and understand their findings.
As promised, here they are, explained in detail.
But first, an important clarification: finding a biological association in an experiment does not necessarily mean that we can apply those conclusions directly to human nutrition.
And that is precisely why these studies deserve a closer look.
1. The Mouse Experiment: What Actually Happened?
One particularly interesting study was published in 1996 under the title Dependence of Photocarcinogenesis and Photoimmunosuppression in the Hairless Mouse on Dietary Polyunsaturated Fat.
The researchers used hairless mice, an experimental model commonly employed to investigate the effects of ultraviolet radiation on the skin.
They prepared five experimental diets, each containing 20% total fat by weight, but with different proportions of polyunsaturated sunflower oil and saturated hydrogenated cottonseed fat.
The proportions of polyunsaturated fat were 0%, 5%, 10%, 15% and 20% of the diet.
The animals were exposed to UV radiation for ten weeks, and tumor development was monitored over the following months.
What did the researchers find?
As the proportion of polyunsaturated fat increased, the severity of the skin carcinogenic response also increased.
The researchers observed differences in:
Tumor incidence.
Number of tumors developed.
Progression from benign tumors to squamous cell carcinomas.
Animal survival.
They also investigated the skin's immune response.
In an acute UV exposure experiment, the diet containing 20% saturated fat provided almost complete protection against suppression of a specific immune response, whereas the diet containing 20% polyunsaturated fat resulted in 57% suppression.
Why does this matter?
Ultraviolet radiation does more than damage DNA. It can also interfere with immune mechanisms involved in recognizing and eliminating abnormal cells.
The researchers suggested that the differences observed might be partly related to UV-induced immunosuppression.
However, these mice primarily developed non-melanoma skin tumors.
This experiment does not demonstrate that polyunsaturated fats cause melanoma.
Original study: PubMed – 1996
2. Another Experiment: Melanoma and Dietary Fat
A separate study published in 1984, Dietary Fat Influences on Murine Melanoma Growth and Lymphocyte-Mediated Cytotoxicity, examined mice implanted with B16 melanoma cells.
The researchers compared different diets and investigated how quickly tumors became visible and how certain immune cells responded.
In one experimental condition, involving the implantation of one million melanoma cells, tumors appeared earlier in mice consuming polyunsaturated fats than in those consuming saturated fats.
Differences in lymphocyte-mediated cytotoxicity were also observed.
These findings suggest that dietary fat composition can influence certain biological conditions associated with tumor growth.
But there is an essential distinction.
The animals were implanted with melanoma cells. The study did not investigate whether consuming a particular oil spontaneously caused melanoma.
Therefore, the findings concern tumor progression in an experimental model, not the risk of developing melanoma from eating a specific food.
Original study: Journal of the National Cancer Institute, 1984
3. The Sydney Study: 100 People With Melanoma and 100 Without
Now we move from animal experiments to human research.
In Sydney, Australia, between 1984 and 1985, researchers collected subcutaneous adipose tissue samples from:
100 patients diagnosed with melanoma.
100 control participants without melanoma.
The study, published under the title Melanoma and Dietary Lipids, investigated the fatty acid composition of adipose tissue.
Why examine body fat?
Because adipose tissue composition can provide information about longer-term exposure to certain fatty acids.
However, it is not a perfect measurement of dietary intake, since metabolism and other biological factors also influence its composition.
What were the results?
The researchers found that the percentage of polyunsaturated fatty acids in adipose tissue was significantly higher among melanoma patients than among controls.
The difference was statistically significant, with p < 0.01.
They also observed that a greater proportion of control participants had low levels of linoleic acid compared with melanoma patients.
The authors proposed that higher polyunsaturated fat consumption might contribute to melanoma development.
Does this mean polyunsaturated fats cause melanoma?
No.
The study identified an association, not a causal relationship.
Other factors, including sun exposure, individual characteristics and lifestyle habits, could have influenced the results.
Furthermore, adipose tissue composition was measured after diagnosis, making it impossible to establish a clear causal sequence.
The study does not demonstrate that someone who consumes more sunflower oil necessarily has a higher risk of melanoma.
Original study: Melanoma and Dietary Lipids – PubMed
4. What Did Later Research Find?
This is where the scientific picture becomes more complex.
Not all subsequent studies reproduced the Sydney findings.
A study conducted in Brisbane, Australia, involving 41 women with melanoma and 297 controls, found an inverse association between polyunsaturated fat intake and melanoma: women reporting higher consumption had a lower risk in that analysis.
Another Italian study involving 51 melanoma patients and 51 controls did not identify a significant association between linoleic acid and melanoma.
An Australian study published in 2006 also found no evidence that higher total dietary fat intake increased skin cancer risk.
Other experimental findings suggest that the specific type of polyunsaturated fat matters.
In a 2011 study, mice fed a diet rich in omega-3 fatty acids from fish oil developed fewer UVB-induced skin tumors than mice consuming an omega-6-rich diet.
This leads to an important conclusion:
Not all polyunsaturated fatty acids behave in the same way, and they should not be treated as a single substance with identical biological effects.
Equally, we cannot conclude that saturated fats protect humans against melanoma.
5. Saturated, Monounsaturated and Polyunsaturated Fats: What's the Difference?
To understand these studies, we need a little chemistry.
Dietary fats contain different fatty acids. Their molecular structures influence their physical properties, chemical stability and biological functions.
Saturated fats
Saturated fatty acids contain no carbon-carbon double bonds.
Their carbon chains are saturated with hydrogen atoms.
They are generally more resistant to certain oxidation reactions, and many saturated fats are solid at room temperature.
Common food sources:
Butter and cream.
Full-fat cheese.
Beef and lamb fat.
Lard.
Coconut oil.
Palm oil.
However, greater chemical stability does not automatically mean better health outcomes.
Monounsaturated fats
Monounsaturated fatty acids contain one carbon-carbon double bond.
One of the best-known examples is oleic acid, an omega-9 fatty acid.
Common food sources:
Olive oil.
Avocados.
Olives.
Hazelnuts.
Almonds.
High-oleic sunflower oil.
Extra virgin olive oil is particularly interesting because, in addition to oleic acid, it contains minor compounds such as polyphenols.
Polyunsaturated fats
Polyunsaturated fatty acids contain two or more carbon-carbon double bonds.
Two important families are omega-3 and omega-6 fatty acids.
Some are essential fatty acids, meaning our bodies cannot produce them and we must obtain them through food.
Common omega-6 sources:
Conventional sunflower oil.
Corn oil.
Soybean oil.
Conventional safflower oil.
Sunflower seeds.
Walnuts.
Common omega-3 sources:
Sardines.
Salmon.
Mackerel.
Anchovies.
Flaxseeds.
Chia seeds.
Walnuts.
It is important to distinguish plant-derived omega-3, mainly alpha-linolenic acid (ALA), from marine omega-3 fatty acids such as EPA and DHA.
They do not have identical metabolic functions.
Also, most foods contain mixtures of fatty acids rather than exclusively one category.
6. Why Are Scientists Interested in Fat Oxidation?
The double bonds present in polyunsaturated fatty acids make certain molecular structures more susceptible to oxidation.
During lipid peroxidation, secondary compounds may form that can react with proteins, cell membranes and other biological molecules.
Some of these compounds participate in processes involving oxidative stress, inflammation and cellular signaling.
This is especially relevant to dermatology because ultraviolet radiation can generate reactive oxygen species and alter membrane lipids.
However, our bodies also possess antioxidant defense systems and repair mechanisms.
Furthermore, polyunsaturated fatty acids perform essential physiological functions.
A fatty acid's susceptibility to oxidation does not, by itself, establish that a food containing it is carcinogenic.
7. So, Which Oil Should We Use?
Current scientific evidence does not justify eliminating vegetable oils rich in polyunsaturated fats or replacing them with butter or animal fat to prevent melanoma.
In fact, the World Health Organization recommends limiting saturated fat intake and replacing some of it with polyunsaturated or plant-derived monounsaturated fats, particularly because of their cardiovascular benefits.
From a practical nutritional perspective, I recommend a varied diet, using extra virgin olive oil as a primary culinary fat within a Mediterranean-style eating pattern and including dietary sources of omega-3 fatty acids.
It is also sensible to avoid repeatedly overheating or reusing frying oils.
There is currently insufficient evidence to recommend restricting omega-6 intake specifically to prevent melanoma.
And, of course, no dietary intervention can replace appropriate sun protection.
8. What Can We Actually Conclude?
FACT: Certain mouse experiments found that dietary fat composition influenced the appearance, progression or growth of skin tumors.
FACT: The Sydney study identified a higher proportion of polyunsaturated fatty acids in the adipose tissue of melanoma patients compared with controls.
FACT: Other human studies did not reproduce that association, and some reported findings in the opposite direction.
INFERENCE: Lipid metabolism may be relevant to understanding certain mechanisms involved in skin carcinogenesis and immune responses.
HYPOTHESIS: The fatty acid composition of the diet might influence biological processes associated with skin cancer under specific conditions.
WHAT WE STILL DON'T KNOW: Whether specifically changing omega-6, omega-3 or saturated fat intake reduces melanoma incidence in humans.
My Final Thoughts
For years, we have learned to care for our skin from the outside: through cosmetics, antioxidants, sun protection and dermatological treatments.
But our skin is a living organ, closely connected to our metabolism, immune system and nutrition.
Research into dietary fats and skin cancer reminds us that there are complex biological mechanisms we are still trying to understand.
And to me, that is one of the most fascinating aspects of science: discovering questions that deserve further investigation.
This is not about being afraid of an oil. It is about understanding what we know, what we suspect and what we have yet to prove.
Paola Gugliotta
Cosmetic Formulation · Skin Science · THE TODAY PROJECT
Scientific References
Reeve et al. (1996). Dependence of Photocarcinogenesis and Photoimmunosuppression in the Hairless Mouse on Dietary Polyunsaturated Fat. PubMed
Dietary Fat Influences on Murine Melanoma Growth and Lymphocyte-Mediated Cytotoxicity (1984). Journal of the National Cancer Institute. Original article
Melanoma and Dietary Lipids. Sydney case-control study involving 100 melanoma patients and 100 controls. PubMed
Diet and Melanoma: An Exploratory Case-Control Study. Brisbane study. PubMed
Serum Fatty Acids and Risk of Cutaneous Melanoma: A Population-Based Case-Control Study. Full text
Association Between Dietary Fat and Skin Cancer in an Australian Population Using Case-Control and Cohort Study Designs (2006). Full text
Effects of High-Fat Diets Rich in Either Omega-3 or Omega-6 Fatty Acids on UVB-Induced Skin Carcinogenesis in SKH-1 Mice (2011). PubMed
World Health Organization (2023). Saturated Fatty Acid and Trans-Fatty Acid Intake for Adults and Children. WHO guidelines
