Is a fast food ingredient killing us?

QUESTION: Hi Dr Zac, After eating fast food I often feel bloated, sluggish, and even a little nauseous. Recently, I’ve seen heaps of wellness influencers blaming seed oils like canola or soybean for inflammation, poor digestion, and overall “toxicity”. Is there actually any science behind this, or is it just another internet scapegoat? – Dani, 32, Albury NSW

ANSWER: Dear Dani, Thanks so much for questioning everything that you see on social media. Seed oils definitely are under the microscope at the moment but before you swear off canola oil let’s have a look at what the research really says. Spoiler, it’s more complicated than the real ingredients found in a cheeseburger or the dressing on your salad.

What exactly are seed oils, and why the backlash?

Seed oils usually refer to those oils extracted from seeds such as canola, soybean, sunflower, corn, or grape seed. These guys are high in polyunsaturated fats, particularly omega six fatty acids like linoleic acid.

The theory goes that too much linoleic acid could turn into inflammatory compounds in the body, which in turn can lead to bloating, gut discomfort, or systemic inflammation. Lots of wellness creators dwell on this but science isn’t quite that clear cut.

A recent study on the Health Effects of Various Edible Vegetable Oils found the evidence to be mixed, and this depended heavily on the oil type, how it’s processed, the person’s diet and also that person’s metabolism.

Another clinical review on Frontiers looked at people with diabetes and dyslipidaemia. This study reported that certain seed oils, including canola, flaxseed, and sesame, sometimes improved lipid profiles, glycaemic control, or oxidative stress. Once again these results were inconsistent.

There was also a large study of nearly 1900 participants published on Science Daily that found that higher blood levels of linoleic acid were actually linked with lower inflammation and better cardiometabolic health. this study challenged the belief that seed oils automatically drive inflammation.

So who should you believe when the evidence goes both ways? Some data suggest seed oils may be neutral or beneficial, while other studies advise caution depending on various factors.

Why fast food makes you feel terrible

Seed oils aren’t necessarily the only culprit for why fast food is making you feel terrible. These meals are a perfect storm of digestive horrors: ultra-processed ingredients, refined carbohydrates, excess salt, trans fats, overcooked proteins, chemical additives, and oils that are often reused or overheated.

Together, these factors can cause oxidative stress, where your body produces unstable molecules that damage cells and spark inflammation, leaving you feeling bloated and sluggish.

If you think seed oils are solely to blame, you are wrong. Many nutrition experts argue that demonising seed oils distracts from the bigger issue: Australia’s love affair with ultra-processed, nutrient-poor foods.

It’s worth remembering that repeatedly heating oils can produce oxidised lipid compounds, which can irritate tissues far more than fresh oils ever would. So, in fast food, it’s often the degraded oil that’s to blame, not the seed oil itself.

Dr Zac’s checklist for eating well:

• Eat more whole foods, less fast food. Nothing beats the basics.

• Use heat-stable oils at home. Extra virgin olive oil or avocado oil are great choices, and avoid reheating oil too often.

• Balance your fatty acids. Include omega-3-rich foods like salmon, chia, and flax to offset omega-6 intake.

• Watch out for other inflammatory triggers. Sugar spikes, processed meats, refined carbs, poor sleep, and stress all add up.

• Check with a professional. Make an appointment to see a dietitian or gastroenterologist who can help identify intolerances or sensitivities with your gut health.

Stay healthy, Dr Zac

Got a question? Email askdrzac@drzac.com.au

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