Trans fats & margarine

Why it matters

Trans fats are the rare food component with essentially no redeeming feature — and direct evidence of hormonal harm. Industrial trans fats (from partially hydrogenated oils) have been linked in research to lower testosterone and reduced sperm count and quality in men, on top of their well-known damage to heart health through inflammation and bad cholesterol. Many countries have now banned or restricted them, which is genuine progress, but they still lurk in some processed baked goods, fried foods and older-style margarines. Unlike most foods here, the right amount of industrial trans fat isn't "moderate" — it's zero.

What's inside

The culprit is industrial trans fat, created by partially hydrogenating vegetable oils to make them solid and shelf-stable. These artificial fats raise inflammation, worsen the cholesterol profile, and — relevant here — are associated with lower testosterone and impaired sperm parameters. There is no nutritional benefit to offset any of this; they exist purely for food-industry convenience.

For men

For men, the evidence is specific and concerning: higher trans-fat intake is associated with lower testosterone and poorer sperm count and quality. Combined with the inflammation trans fats cause — which itself interferes with healthy hormone signalling — this makes them uniquely worth eliminating. There's no downside to cutting them to zero.

For women

For women, trans fats drive the inflammation and metabolic harm that work against hormonal balance, and they're linked to worse fertility outcomes. As with men, because they offer nothing nutritionally, the goal is simply to avoid them — a clear, no-trade-off improvement.

How to eat it

Read labels and avoid anything listing "partially hydrogenated oils." That mainly means steering clear of certain processed baked goods (some pastries, biscuits, cakes), deep-fried fast food, and old-style hard margarines. Modern soft spreads are mostly trans-fat-free now, but checking is worthwhile. Cooking with stable natural fats — olive oil, butter — sidesteps the issue entirely.

Worth knowing

Note the distinction: the tiny amounts of natural trans fats in dairy and meat are not the concern — it's the industrial trans fats from hydrogenation. Thanks to regulation they're far less common than a decade ago, but not gone. This is one of the few items where the recommendation is genuinely "avoid," not "moderate."

Bottom line

Industrial trans fats directly lower testosterone and harm sperm with zero nutritional upside — making them the one item on this list to avoid entirely rather than merely limit.