Longan

good source of vitamin C, B-vitamins and potassium, copper, zinc, magnesium, phosphorus, iron, calcium and manganese.

longan fruit is used for treating and managing anemia, iron deficiency, skin issues, stress, insomnia, high blood pressure, obesity, chronic diseases and helps in boosting immunity, speeding up the healing process, aiding digestion and improving memory capacity. 

synthesizes collagen and keeps skin firm.
protects skin from ultraviolet radiation and also gradually reverses wrinkles, fine lines, dark spots, blemishes, pigmentation, etc.
its leaf and peel polyphenols protect the collagen and elastin scaffolding in skin and tissue by blocking the enzymes that break them down (collagenase, hyaluronidase, MMPs), and they raise the body's antioxidant defenses like glutathione. the pulp fibers also feed good gut bacteria, which matters for healthy aging.

longan helps you stay asleep longer, but it doesn't knock you out.
the flowers turn on these enzymes: TPH1, DDC, AANAT, ASMT. they convert into serotonin and then into melatonin. so instead of just suddenly taking melatonin and falling asleep, you're just building more melatonin naturally within your body.
takes 1-2 weeks of daily use before the effect shows, unlike a melatonin pill that works the first night. so it's lowkey kinda mid for that but it's yummy and natural.

so longan is good for retaining or enhancing memory.
acetylcholine is the neurotransmitter you need to encode new memories, right? but acetylcholinesterase destroys acetylcholine.
well longan blocks acetylcholinesterase, meaning you get to keep producing acetylcholine and continue to encode new memories.
it supports neuron survival and new neuron growth (shown with raised BDNF), and its polyphenols lower brain oxidative stress and neuroinflammation.
traditionally taken to settle a racing mind, ease anxious restlessness, quiet heart palpitations tied to worry, and sharpen memory dulled by exhaustion.
use the dried aril simmered into a tea or tonic soup, 9 to 15g, in the evening.

kills ovarian, nasopharyngeal, liver, lung, stomach, and colorectal cancer cells.
in colorectal cancer it shuts down Bcl-2, the protein cancer cells use to refuse the order to die, which forces apoptosis.
in ovarian cancer the polysaccharide kills the cells directly AND activates your own macrophages, B cells, and T cells at the same time.
corilagin from the seed also made a standard chemo drug (5-fluorouracil) hit ovarian cancer cells harder.
Longan seed ethanolic extract: 156 mg ellagic acid and 23.3 mg gallic acid per 100 seeds.
seed polyphenols block angiogenesis (tumor blood supply) and stop cancer cells from migrating.
the anticancer parts are the seed, the peel, and the flower. the part you eat is the weakest part. eating longan is not the same intervention.
it's just some studies i found on longan, but since the seeds are poisonous, don't use it unless you're a scientist experimenting ig. oh and talk to your oncologist before using any concentrated seed or peel extract during cancer treatment, since it can interact with chemotherapy.

longan is an appetite regulator, not a fat burner.
the antidiabetic action is in the PEEL, SEED, and FLOWER, not the sweet fruit.
the seed slows carb digestion (alpha-glucosidase inhibition), the peel supports the body's own insulin production, and the flower extract dials down fat-building genes and fat absorption.
longan flower water extract reduces hyperlipidemia and obesity markers by downregulating SREBP-1c and FAS (lipogenesis genes) and reducing exogenous lipid absorption.
the dried sweet aril, on the other hand, is loaded with natural sugar and will RAISE blood sugar, so diabetics should treat dried longan like candy and keep it small.

longan seed and peel extracts slow melanin production by blocking tyrosinase (the enzyme behind dark spots), so topically they can help fade uneven pigmentation and brighten tone.

builds bone and slows bone loss.
it switches on osteoblasts, through the RUNX2 master switch. also switches on the cartilage-building genes (sox9, aggrecan, collagen II), while turning down the bone-eating cells (osteoclasts, via NF-kappaB).
good for osteoporosis and bone-density support, postmenopausal bone loss, cartilage and joint support, fracture-recovery support, and healthy skeletal aging. use the pulp or seed extract.

tldr:
https://www.organicfacts.net/longan-fruit.html

while longan seeds have been used in tcm, don't confuse longan with lychee, because lychee seeds are dangerous. lychee seeds and unripe fruit carry hypoglycin A, which caused fatal blood-sugar-crash brain swelling in kids in India and Vietnam. but rambutan seeds are fine roasted.
If I had to choose between rambutan, lychee, or longan, I would pick rambutan all day, simply cuz it tastes better. Although it's hairy and messy to process, it's sweeter, has a better flavor and has more flesh.