Non-sweet fruits are often thought to be as healthier than their sweet counterparts. This is due to the misconception that sweet sugars in fruits are harmful. From a biological perspective, this assumption is not plausible – quite to the contrary! Find out why non-sweet fruits actually are…
For the quick reader:
Are Non-Sweet Fruits Healthier than Sweet Fruits?
No. Sweet fruits are essential for human health, while most non-sweet vegetable fruits are not edible in nature. The wild-type fruits of most non-sweet fruits naturally contain potent toxins. The two most prominent toxic compounds in vegetable fruits are cucurbitacin and solanine. Humans can only safely eat the fruits – of those otherwise toxic plants – due to selective breeding. Though the decreased toxic loads are enough for the fruits to become palatable for humans, they are not entirely eliminated! This shows that non-sweet fruits have not evolved as human (or mammal) food source.
In contrast, most sweet fruits – especially tropical fruits – are edible for primates (including humans) in the wild – because they are our biologically appropriate foods: humans have co-evolved with those fruits as the primary food source (read more here).
It is not surprising that it turns out that sugar from sweet fruits is actually healthy. So isn’t it ironic that the newest diet trend is to avoid sweet fruits!? But let’s elaborate more in-depth:
Non-sweet vegetable fruits
Sweetness is the ultimate character we associate with fruits. But not all fruits are sweet! Non-sweet fruits are often categorized as vegetables because we use them for cooking and in salads. In actuality, many of our daily vegetables are botanically fruits and belong to the two plant families Solanaceae and Cucurbitacea:
- Bell peppers
- Chilli peppers
Why are “vegetable fruits” fruits not sweet?
Evolution’s short answer is that non-sweet fruits have evolved with fruit-eating birds. Birds are not appealed by sweet taste (they cannot even taste sweetness).
Sweet fruits have evolved with frugivores (fruit-eaters) that are appealed by sweet, i.e., mammalian frugivores, including primates (chimpanzees and humans are included). Non-sweet fruits only became human food recently through extensive cultivation and breeding for bigger, sweeter, and less toxic fruits.
In contrast – but not surprisingly – many tropical fruits are much sweeter, less acidic, and more fleshy – because they have naturally evolved as monkey, ape, and human food and have co-evolved with us primates.
Nightshade family (Solanaceae)
Originally, the group of nightshade veggies (tomatoes, bell peppers, and eggplants) was deadly toxic! They contain the toxic solanin. Green tomatoes should not be eaten because the solanin content is too high!
Gourd family (Cucurbitacea)
The plant family of cucumbers, pumpkins, and squash has bitter tasting cucurbitacin that signal toxicity to humans – tasting bitterness and toxicity, is crucial for survival and health of animals!
The bitter toxin can kill a human, when the off-putting taste of Cucurbitacea vegetables is ignored, like the case of a german gardener that died of courgette-poisoning (zucchini) and made it to the Newspapers in 2015!
“Although modern seed hybridising has bred the naturally-occurring toxin cucurbitacin out of cucumbers, pumpkins and squash it’s possible, through a rare mutation and back-crossing, for it to return. Home vegetable growers who repeatedly grow only their own collected seed run the risk of this occurring.”www.gardendrum.com
Are our veggies pre-historic foods for huge herbivores?
It is an evolutionary rule called the “dispersal syndrom“, that fruits are nontoxic, beneficial and nutritionally suitable for their mutualistic seed dispersing partner (animal). But not to animals that are not their seed-disperser!
So why is the gourd family so toxic to humans in their natural state? Humans are certainly not the original consumer and seed disperser of the wild gourd family fruits. But who is? It seems they were the food of the extinct megafauna – which makes those veggies the food of ancient giant beings:
“Directly, megafauna consumed Cucurbita fruits and dispersed their seeds; wild Cucurbita were likely left without mutualistic dispersal partners in the Holocene because they are unpalatable to smaller surviving mammals with more bitter taste receptor genes.” (Kistler et al., 2015)
Are non-sweet fruits healthier than sweet fruits?
This is a common belief and is simply not true. Vegetable fruits can be a valuable addition to the human diet, especially in temperate climates. However, they are not more healthy for humans than sweet fruits!
Humans are anatomically and physiologically adapted to eating a large amount of sweet fruit in their diet – which is shown by our love for sweetness! It is even a consensus in nutrition and health science that sweet, simple sugar in fruits is not harmful but brings various health benefits! Fruits are highly nutritious and build the basis of a biologically appropriate diet for high fruit-eating species – like ourselves!
Natural diet of frugivorous primates: Ripe (tropical) fruits make up the bulk part of the species-specific diet of frugivorous primates. This means fruit is not the only food in their diet, but the most in terms of quantity (around 70% for chimpanzees). Depending on the season, frugivorous primates eat those fruit types, which are ripe and sweet, and only resort to other food groups when they are scarce.
Instinctual behavior of humans: Humans are attracted to colorful fruits, and loves sweet. In fact, most other mammals cannot see as many colors and cannot taste sweetness like humans do. Those are traits that have evolved in frugivores for fruit foraging! When we observe small children’s natural, instinctive eating behavior because they are not so culturally “confused”: If small (!) children are given bowls with different foods, it is the sweet fruit that is eaten first.
Why do fruits contain sugars in general?
Fruits are the seed-containing parts of a plant that develop from a flower. The seeds within fruits carry the embryo of the plant. Fruits are the part that ensures the dispersal of the next generation, which is sexually reproduced. In contrast to plant growth and offshoots, seeds carry new genetic variations of two parent plants.
Fruits have evolved as the plant part that ensures seed dispersal by fruit-consuming animals (frugivores). The sweet sugar (energetic nutrition) of fruits is the pay-off for the mobilization offered by the animals.
All fruits contain simple sugars
All fruits contain a certain amount of sugar, also the non-sweet ones. This sugar is present either in the form of fructose or glucose. Some people believe that fruit sugar is unhealthy, but quite to the contrary, sugars from fruits are the perfect energy nutrition for our cells: humans are biologically adapted to sweet taste and eating sweet fruits. Furthermore, fructose does not even require insulin to enter our cells. Read more here on the long-held misconception about sugar.
Fruits are intended to be eaten from the matching consumer!
Sugars in fruits are the nutritious reward of the seed-dispersing animal – the fruit-eating animal or frugivore. To attract seed-dispersers, the plant evolved a fleshy, nutrition-rich part appealing to the right frugivore – its fruits.
Eating fruit is a symbiosis between plants and fruit-consuming animals. But it is important to note that only the animal that is a matching seed disperser – the ones that have co-evolved with a particular fruit as a food source.
Why is this relevant when we look at the health benefits of different fruits? Because plants do evolve toxic defense within their fruits against the “wrong” fruit consumers – in the case of “bird fruits”, we are those wrong consumers.
Most fruits from temperate climate have evolved as bird foods
Most wild-type fruits in temperate zones (including temperate sweet-sour fruits and vegetable fruits) are not sweet but perfect bird food. This is because birds do not have sweet receptors like mammals and eat most of the canopy berries in a temperate climate.
The crabapple – the original apple – is tiny and very sour.
Most temperate fruits we know today originally evolved with birds as their fruit-disperser. This is why they are not sweet (Except for nectar-eating species, birds cannot taste sweetness, but acidic taste).
Humans have evolved with tropical sweet fruits – not with vegetable fruits
Humans originated in tropical forests. Our biology is still highly similar to today’s tropical frugivorous primates. Thus tropical fruits are our “evolutionary foods”.
In contrast to complex carbs in grains, simple sugar molecules in fruits taste sweet and are tasty for us in their raw form (read here about fruits vs. grains carb source). Humans and other primate frugivores have evolved to taste and love sweet, simple sugars to obtain energy from fruits while helping the plant to disperse into new areas!
The idea of non-sweet vegetable fruits being healthier than sweet fruits is simply untenable from an evolutionary and ecological view. The war on natural simple sugars and ignoring the crucial role of sweet tropical fruits in health goes against human dietary biology and evolutionary adaptations.
Read more about the biological suitability of different foods for humans:
Go To What Food Are Really Suitable for Humans?
For more information on how to adopt a high-fruit diet, check out our guide here:
Go to How to do the Frugivore Diet
- D. Sharma, S. Mishra, An Acute Toxicity in Human Health of Raw and Cooked Vegetable in Tomato and Spinach. Longdom: Journal of Nutrition and Food Sciences (2021) (available at https://www.longdom.org/open-access/an-acute-toxicity-in-human-health-of-raw-and-cooked-vegetable-in-tomato-and-spinach-64567.html).
- A. Fischer, Y. Gilad, O. Man, S. Pääbo, Evolution of bitter taste receptors in humans and apes. Molecular Biology and Evolution. 22, 432–436 (2004), doi:10.1093/molbev/msi027. (link)
- Pat Hagan, You could be eating killer courgettes. Daily Mail Online (2020) (available at https://www.dailymail.co.uk/health/article-8676819/You-eating-killer-courgettes.html). (link)
- German man dies after eating home-grown zucchini. GardenDrum (available at https://gardendrum.com/2015/08/25/german-man-dies-after-eating-home-grown-zucchini/). (link)
- K. Valenta, O. Nevo, The dispersal syndrome hypothesis: How animals shaped fruit traits, and how they did not. Functional Ecology. 34, 1158–1169 (2020), doi:10.1111/1365-2435.13564. (link)
- L. Kistler et al., Gourds and squashes (Cucurbita spp.) adapted to megafaunal extinction and ecological anachronism through domestication. Proceedings of the National Academy of Sciences. 112, 15107–15112 (2015), doi:10.1073/pnas.1516109112. (link)