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Why soybean oil leads to inflammation, weight gain: A dietician explains the science

Rather than depend on one popular oil, it is better to rotate oils according to cooking needs

3 min readUpdated: Dec 9, 2025 06:28 PM IST

Soybean oil requires high-heat chemical processing for extraction, which makes it cheap but it also changes the structure of fatty acids.

Written by: Simrat Kathuria

Soybean oil is currently under the scanner as a cooking medium because of its fat profile, inflammatory potential and the effect of heat on it. Many of us took to using it because of the price, easy access and the marketing that brought soybean oil at the top. On paper, the composition looks acceptable: it contains omega-6 fatty acids, vitamin E and minimal saturated fats. But modern nutrition looks beyond basic labels. The real concern lies in the ratio of fats, oxidative stability and how chemical reactions affect human metabolism.

Soybean oil requires high-heat chemical processing for extraction, which makes it cheap but it also changes the structure of fatty acids. The process of heat may include oxidation, which will produce free radicals that will have to be neutralised by the body. When the oil is used for deep frying or heating repeatedly, it breaks up faster, producing compounds, which are associated with inflammation.

The Omega-6 problem: When healthy fats turn harmful

Omega-6 fatty acids are essential but the key word is balance. A good, healthy diet has an omega-6 to omega-3 ratio of about 4:1 or even less. But unfortunately, soybean oil creates a ratio of 20:1, which is very disturbing for metabolic balance. Excessive intake of omega-6 leads results in pro-inflammatory compounds which trigger abdominal weight gain, joint inflammation, insulin resistance and increase triglycerides.

Considering most Indians are already consuming Omega-6 through refined snacks, bakery products, namkeen and restaurant foods, soybean oil adds to the imbalance.

What happens when soybean oil is heated?

Most Indian cooking involves high heat, tadka, frying, roasting, pushing oils to their thermal limits. Soybean oil has a moderate smoke point but the real issue isn’t smoke; it’s oxidative instability. Under high heat, it produces lipid peroxides that are associated with cellular damage, aldehydes that increase neurological and cardiovascular risks. On repeated heating, it forms traces of trans-fats. These by-products may be invisible in your kadai, but they create inflammation in your body over time.

What’s the gut-hormone connection?

More recent findings suggest that soybean oil, by its fatty acid makeup, could be a cause of intestinal permeability and hormonal disturbance. Omega-6 has been found to change the balance of gut bacteria, which in turn influence digestion, immunity and appetite control. For women suffering from PCOS, thyroid problems or insulin issues, this cycle of inflammation can worsen symptoms.

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But isn’t soybean oil high in Vitamin E, which is an antioxidant?

Vitamin E can indeed protect the body from oxidation but is not available in sufficient amounts. It is through the refining processes and cooking that the natural antioxidant value is reduced to a great extent.

The actual issue is not the soybean plant; it is the chemically extracted and industrially refined oil, along with its specific characteristics that are not suitable for Indian cooking. Rather than depend on one “popular” oil, it is better to rotate oils according to cooking needs.

A small change like choosing more stable, nutrient-rich oils can make a difference in improving digestion, reducing inflammation and promoting long-term metabolic health.

(Kathuria is a clinical dietician)