Lemon Juice / Vitamin C

The single most impactful thing you can do for a plant-based diet is squeeze lemon on it -- 50mg of vitamin C (roughly one lemon) can increase iron absorption from legumes and grains by 3-6x.

Why It Matters for Longevity

Fontana gives lemon juice a specific, daily prescription: juice of one lemon per day, used to cook and season vegetables, legumes, and grains. This is not about flavour (though it helps). It is about solving the critical mineral absorption problem that comes with plant-forward eating.

Plant foods contain non-heme iron, which is bound by phytates, oxalates, and fibre into complexes the gut struggles to absorb. Vitamin C breaks these bonds. It reduces ferric iron (Fe3+) to ferrous iron (Fe2+) -- the form your gut can actually take up -- and chelates both iron and zinc into more bioavailable forms (Refs 101, 102). The effect is dramatic: Hallberg et al. (1989) showed that 50mg of ascorbic acid increased non-heme iron absorption by 3-6x when consumed at the same meal. Timing matters -- the vitamin C must be present in the gut simultaneously with the iron source.

This has real clinical implications. Iron deficiency is the most common nutritional deficiency worldwide, and it disproportionately affects people eating plant-based diets. Fontana notes this is especially important for vegetarians and vegans whose iron and zinc from plant sources is inherently less bioavailable. The fix is simple and delicious: a lemon squeeze on your lentils.

Beyond mineral absorption, vitamin C itself is a potent antioxidant that Fontana cites for neutralising free radicals and preventing LDL oxidation (Refs 22-24). A review by Carr & Maggini (2017) confirmed that 100-200mg daily supports optimal immune function, including epithelial barrier integrity and enhanced neutrophil and lymphocyte activity.

There is also an intriguing synergy with green tea. Green et al. (2013) showed that adding citrus juice stabilised tea catechins in the alkaline gut environment, potentially increasing EGCG bioavailability by up to 6x. So a squeeze of lemon in your green tea is not just a taste preference -- it is a pharmacokinetic strategy.

Fontana also warns about the opposite effect: tea, coffee, and cocoa consumed during meals reduce mineral absorption, working against the vitamin C benefit. The practical takeaway is to drink tea between meals and use lemon during meals.

How to Use It

Squeeze fresh lemon juice over every meal containing legumes, grains, or greens. Use it to dress salads (with olive oil), season cooked vegetables, brighten soups, and finish grain bowls. Add to green tea for catechin stabilisation. Use the zest too -- it concentrates limonene, a compound that promotes detoxification enzymes. One lemon per day is Fontana's specific recommendation. Juice at the last moment; vitamin C degrades rapidly with air exposure.

What to Pair It With

Flavor Profile

Sharply sour and bright with a clean acidity that cuts through richness and lifts other flavours. The aroma is instantly recognisable -- zesty and fresh from volatile essential oils, especially limonene. The juice has a thin, slightly viscous quality. The peel and pith add subtle bitterness and intense aromatic complexity. A small amount transforms a dish without dominating it, which is why nearly every cuisine uses citrus acid as a finishing element.

The Science

• Hallberg et al. (1989): 50mg ascorbic acid increased non-heme iron absorption 3-6x in controlled meals
• Carr & Maggini (2017): 100-200mg/day vitamin C optimal for immune function and infection prevention
• Green et al. (2013): citrus juice stabilised green tea catechins, increasing EGCG bioavailability up to 6x
• Fontana: juice of 1 lemon daily with meals containing legumes, grains, vegetables (Refs 101, 102)

Key Nutrients