I couldn't find a lot on this subject when I went looking, so I'm basically just writing my findings in case they're useful for anyone else. I'll go over some of the science, then break down the major groups, and then for each group I'll add what the studies suggest and how to hit the goal on keto.

Skip to the end if you just want some shopping advice. These are my targets based on the papers, they're not gospel and many are above RDAs (which tend to lag the papers).

None of this is medical advice, this represents my best understanding of the ~600 papers I've read, and targets I've set in line with those papers. I am not a doctor, and definitely not your doctor.

Overview: It's More Complicated Than You Think

There's a lot of hype about antioxidants: "free radical fighters", ORAC scores, superfoods. I wanted to dive into what's actually supported by the data and what's just marketing hype.

Most of what's labelled as "antioxidant activity" in foods is actually downstream signalling: some substances cause an increase in the activity of the Nrf2 (Nuclear factor erythroid 2-related factor 2) pathway, which causes your body to increase production of its own endogenous antioxidants.

Baseline Nrf2 activation is naturally low, because it's tied up with a protein called KEAP1. KEAP1 is studded with reactive cysteine residues; those reactors detect oxidative stress and release Nrf2, which binds DNA at sequences called Antioxidant Response Elements (AREs).

The activation pathways are interesting because they're mostly mild stressors from diet, exercise and heat/cold exposure.

It's worth mentioning chronic constitutive Nrf2 activation is not universally good. Some cancers lock the pathway 'on' in order to hijack the system to survive chemotherapies by repairing the systemic oxidative stress. It's supposed to be pulsatile, activated by intermittent stressors and then returning to baseline. Daily exposure through diet & exercise is the regimen supported by the science, not megadosing activators continuously.

Vitamins & Minerals

While some vitamins & minerals act as direct Nrf2 activators -- particularly Vitamin D, Vitamin E (especially non-alpha forms), Zinc, and Selenium, most play a supporting role.

Selenium is the cofactor for the glutathione peroxidase family and thioredoxin reductase. Nrf2 induction does very little good if you're selenium deficient, because the enzymes can't function.

Copper, zinc, and manganese are cofactors for the SOD enzymes. Iron, Magnesium, Riboflavin (B2), and Niacin (B3) are also essential parts of the glutathione production & recycling pathway.

Vitamin D (target 2000-4000 IU/day): the main source is sunlight, but oily fish does have non-negligible quantities -- wild-caught salmon (600-1000 IU/100g), Atlantic mackerel (350 IU/100g) and canned sardines (270 IU/100g) are standouts. UV-exposed mushrooms (check the label) contain 1000-2000IU/100g. Supplementation is another option.

Vitamin E (target 15mg/day): sunflower seeds (14.6 mg/56g), almonds (14.4 mg/56g), hazelnuts (8.6 mg/56g), avocado (2.7 mg/medium), spinach (3.7 mg/cup cooked) and olive oil (1.3 mg/tsp) are all good sources. Supplementation not recommended, especially for smokers.

Zinc (target 11-15mg/day): oysters (37-74 mg/85g), crab (6.5 mg/85g), lobster (3.4 mg/85g), pumpkin seeds (4.4 mg/56g) and cheddar (1.8 mg/56g) are good sources. Bivalves and crustaceans are the powerhouse here but oysters once a month solves zinc.

Manganese (target 3mg/day): dietary deficiency is genuinely rare, a 56g portion of most nuts or seeds will hit your daily target, spinach is a good source, 5 cups of tea will hit your daily target.

Selenium (target 55-100mcg/day): brazil nuts (70-90 mcg/one nut), tuna (92 mcg/85g), sardines (45 mcg/85g), salmon (40 mcg/85g) and eggs (15 mcg/one medium) are good sources.

Iron (target 8 mg/day for men, 18 mg/day for pre-menopausal women): almost impossible not to hit this on keto if you eat meat or fish.

Magnesium (target 420-500mg/day): you all know this one from the electrolytes page; pumpkin seeds (336 mg/56g), almonds (152 mg/56g), cooked spinach (156 mg/cup), avocado (58 mg/one medium) all work well. Supplementation is an option, it's hard to dose too highly unless you have kidney problems.

Vitamin B2 (target 1.3mg/day): beef liver (2.5 mg/85g), lamb kidney (3mg/85g), chicken liver (1.5mg/85g), spinach (0.43mg/cup), salmon (0.4mg/85g) and mackerel (0.4mg/85g) are good sources. Despite being a B vitamin, this isn't 'free' on keto the way B3/B6/B12 are. You can supplement.

Vitamin B3 (target 16mg/day): almost impossible not to hit if you eat meat or fish.

Carotenoids

Carotenoids split into two functional groups that matter: provitamin A carotenoids (beta-carotene, alpha-carotene, beta-cryptoxanthin) which the body converts to retinol (Vitamin A), and non-provitamin A carotenoids (lycopene, lutein, zeaxanthin, astaxanthin) which act as antioxidants. We're focusing on the second group for this post.

Carotenoid absorption requires fat, not usually an issue on keto but if you're eating these as stand-alone snacks, you'll get lower absorption.

Lycopene (target 8-15mg/day for cardiovascular health): sundried tomatoes (26 mg/56g), chopped tomatoes (19mg/200g), and tomato paste (13.8 mg/2 tbsp) win the day here. The tl;dr is eat tomatoes.

Lutein and zeaxanthin (target 6-12mg/day consumed for macular health): leafy greens have huge absolute numbers here, but poor absorption -- a cup of cooked spinach/kale can have upwards of 20mg. Egg yolks have about 250mcg/egg, but very high absorption, so really they count for a lot more. Pistachios (2.8mg/56g) and zucchini (4mg/cup) round out the options.

Astaxanthin (target unknown but supplement studies use 4-12mg/day): salmon (0.5-3.8mg/100g) and trout (0.5-1.5mg/100g) are the main hitters here. Astaxanthin is the most proven carotenoid in vitro for antioxidant effects. I supplement this at 12mg/day.

Polyphenols

Polyphenols make up the largest and most hyped group of antioxidants. There are thousands of individual compounds, but they can largely be broken down into a few distinct groups.

The most defensible data is that below 500mg/day total polyphenols/day from food correlates with worse cardiovascular and mortality outcomes, and above 1500mg/day delivers diminishing returns if any.

Flavanols / catechins (target 250-400mg/day): green tea (200-300mg/mug), matcha powder (60-100mg/1g), black tea (100-150mg/mug), raw cacao nibs (200-300mg/15g), 85%+ dark chocolate (125-200mg/15g) dominate here. Casein blunts absorption, don't eat with yogurt.

Flavonols: capers (18mg/1 tbsp), red onions (25mg/60g), green tea (7mg/mug), cooked kale (30mg/cup) and broccoli (5mg/cup) are the best options. These numbers look low but flavonols are essential for mast cell stabilisation**,** xanthine oxidase inhibition (protective against gout & hyperuricemia) and killing senescent cells.

Anthocyanins (target 100-200mg/day): blackberries (125mg/75g), blueberries (120mg/75g), red cabbage (80mg/cup), black olives (40-50mg/30g), strawberries (30mg/75g) and raspberries (25mg/75g) lead here for keto-friendly foods. Aronia & maqui powders are net carb friendly (50-200mg/tsp) but bioavailability is lower.

Phenolic acids: coffee is the main keto source here at ~200mg/cup black, artichoke hearts at ~75mg/50g are meaningful too.

Lignans: main keto sources are ground flaxseeds (85mg/tbsp) and sesame seeds (30mg/tbsp).

Olive polyphenols: green olives (70mg/30g) and black olives (50mg/30g) are the main sources. High end EVOO (this will have the polyphenol content labelled on it) can be 30-80mg/tbsp, but this isn't the grocery store stuff and it's very expensive.

Dried herbs & spices have very high levels of polyphenols. Per teaspoon, cloves (320mg), turmeric (120mg), oregano (60mg), rosemary (55mg), thyme (50mg) and sage (30mg) all add meaningful polyphenols to your diet. Pecans (550mg/28g) and walnuts (500mg/28g) are also meaningful contributors.

Endogenous/Thiol System

The endogenous thiol system is the part of the antioxidant story that actually does most of the work in your cells, everything else is supporting cast. Glutathione (GSH) is the master antioxidant in your body, and it's made up of cysteine, glycine & glutamate.

Cysteine (target 1.5-2.5g/day) is the rarest sulfur-based amino acid in the diet. Pork (400mg/100g), beef (350mg/100g), chicken breast (300mg/100g), oily fish (250mg/100g) and eggs (140mg/medium) are the main dietary sources of cysteine. Whey protein (600mg/28g) and NAC (~450mg/600mg pill) are supplemental sources.

Your body can also convert methionine to cysteine inefficiently, it's found in Brazil nuts (one nut covers a lot), sesame seeds, eggs, meat, and fish.

Glycine (target 7-12g/day): another difficult target to hit, but meaningfully supported by the science. It's mostly found in the connective tissue that modern diets throw away: skin, bones, cartilege.

Pork crackling is a heavy hitter at 3g/28g (Asian salted fish skin chips are similar), salmon (~1.5g/100g skin-on), chicken (~1.5g/100g skin on), anchovies (~0.8g/50g) and lean meat/fish (~1g/100g) round out dietary options. Glycine powder & collagen peptides (about 30% glycine by weight) are good options too.

Glutamate is rarely or never the limiting factor, about 20% of protein is glutamate residues. Unless you're eating a very low protein diet (rare on keto), this one is basically free.

Target Summary

This is the list of non-trivial antioxidants that are reasonable to hit on diet alone:

• Vitamin E - 15mg/day (105mg/week)
• Zinc - 11mg/day (77mg/week)
• Selenium - 55mcg/day (385mcg/week)
• Vitamin B2 - 1.3mg/day (9.1mg/week)
• Lycopene - 8mg/day (56mg/week)
• Lutein & zeaxanthin - 10mg/day (70mg/week)
• Polyphenols - 1500mg/day (10,500mg/week)
• Flavanols - 250mg/day (1,750mg/week)
• Flavonols - 15mg/day (105mg/week)

And these are where I'd look to mix diet & supplementation:

• Vitamin D - 1000IU/day (7000IU/week)
• Magnesium - 500mg/day (3500mg/week)
• Astaxanthin - 12mg/day (84mg/week)
• Anthocynanins - 200mg/day (1400mg/week)
• Cysteine - 1.5g/day (10.5g/week)
• Glycine - 7g/day (49g/week)

Weekly Shop

This is an example antioxidant package for a week. There are many like it but this one is mine:

• 18 eggs
• 50g almonds
• 100g caviar/salmon roe
• 100g anchovies
• 100g sunflower seeds
• 100g walnuts
• 25g brazil nuts
• 300g blackberries
• 150g raspberries
• 200g baby spinach
• 200g cavolo nero
• 200g asparagus
• 1/2 head broccoli
• 2 red bell peppers
• 80g capers
• 1 red onion
• 250ml EVOO
• 50g 90% dark chocolate
• 100g cacao nibs
• 35 tea bags (5 cups/day) - mix of herbal and green
• 400g crab
• 400g wild salmon (skin on)
• 200g rainbow trout (skin on)
• 400g chopped tomatoes

Total is about 125g net carbs/week or 17.8g net carbs a day and provides:

• Vitamin E - 136mg/wk
• Zinc -74mg/wk (rest of your food will fill in the missing 3mg)
• Selenium - 915mcg/wk
• Vitamin B2 - 10.3mg/wk
• Lycopene - 52mg/wk, slightly under but very close
• Lutein & zeaxanthin - 54mg/wk but egg 4-9x bioavailability means this hits the target practically
• Polyphenols - 16,500mg/wk
• Flavanols - 6,400mg/wk
• Flavonols - 265mg/wk
• Anthocyanins - 600mg/wk

For supplements, I like to add:

• N-Acetyl Cysteine [NAC], 600-1800mg/day (covers cysteine needs)
• Glycine, 3g/day (tops up glycine to healthy levels)
• Astaxanthin, 12mg/day
• Vitamin D, 2000 IU/day (summer), 4000 IU/day (winter)
• 1 tsp maqui powder/day (tops up anthocynanins to >200mg/day)
• Magnesium glycinate or citrate, 200mg/day

I hope this helped someone who's also been down this rabbit hole.