Is dietary spermidine just as good as a supplement?
No study has yet directly compared dietary spermidine with supplements, and with supplements it remains unclear whether the substance actually reaches the blood adequately. If you want to obtain spermidine, focusing on spermidine-rich foods (such as wheat germ and legumes) is for the time being the most logical choice.
Dietary spermidine is associated in observational studies with lower blood pressure, fewer cardiovascular diseases and better cognitive scores in older age. These are encouraging associations, but not proof that spermidine itself is the cause. Food sources such as wheat germ, mushrooms and legumes deliver spermidine together with dozens of other substances, and it is difficult to determine what exactly is responsible for the effect.
The big question mark with supplements is absorption into the blood. In a small study involving five healthy men, the amount of spermidine in the blood did not rise measurably at all after taking a spermidine supplement. That is a serious signal: if the substance does not reach your blood, it is questionable whether it works in your tissues. The same study did observe reduced inflammatory markers in the blood, but the supplement contained multiple substances at the same time, so spermidine itself cannot be credited for that.
Animal research shows that spermidine activates cellular 'self-cleaning' (autophagy) and protects the heart against ageing and high blood pressure. That is biologically plausible and consistent, but it is animal research. Whether that effect can be replicated in humans via a supplement has not been demonstrated.
Interestingly, your gut bacteria themselves also produce spermidine. Certain bacteria and yeasts produce spermidine in the gut and in this way influence the gut wall. Whether the gut microbiome can be steered via probiotics to produce more spermidine has not yet been systematically studied in humans.
A direct comparison between dietary spermidine and supplements simply does not exist. Reviews conclude that larger, well-designed studies are needed to establish bioavailability, efficacy and optimal dosage. Spermidine is considered safe for the time being, but formal safety data from large studies are still lacking.
No direct comparative study is available. The basis consists of observational studies in humans, a small pilot study (n=5) with supplements, animal experiments and reviews. The total number of participants in human studies is very limited.
What is spermidine and where is it found?
Spermidine is a molecule that occurs naturally in your body, declines with age, and that you also obtain through fermented foods and through your gut bacteria. Whether you should take extra amounts of it is a separate question; what it is and where it comes from is reasonably well described.
Do antioxidant supplements make sense?
For healthy people, antioxidant supplements such as beta-carotene and vitamin E are not useful as protection against cancer or heart disease, and beta-carotene is frankly inadvisable for (ex-)smokers. The only well-supported exception is the AREDS formula for advanced macular degeneration: discuss this with your ophthalmologist.
Are smoothies and fresh juice just as healthy as whole fruit?
Whole fruit beats fruit juice: more fibre, greater satiety and fewer free sugars. Smoothies fall somewhere in between, but are not equivalent to whole fruit either.
Does extra protein help with losing weight without losing muscle?
Extra protein helps preserve muscle mass while losing weight, but works best in combination with resistance training. Aim for 1.6-2.4 g per kilogram of body weight per day, and make sure to train alongside it.
Is taking extra vitamin C worthwhile?
Extra vitamin C offers little benefit for most people. Intensive athletes and people following a carnivore diet do have a good reason to supplement, and those who take it daily tend to experience slightly milder symptoms when they catch a cold.
Does a fasting-mimicking diet work better than simply eating less?
There is currently no convincing evidence that a fasting-mimicking diet works better than simply eating less. For weight loss and metabolic improvement, both strategies appear comparable; choose whichever you can sustain best.