Diet fads have been around for decades including all fruit diets or some variation thereof.
On the surface a fruitarian diet seems OK, I mean its fruit and fruit is good for us right? In fact all governmental nutrition recommendations from around the world include fruit as part of their guidelines for healthy eating.
Fruit has all the good stuff we like to talk about such as fiber, vitamins and minerals, as well as, all the buzz words that are marketed to the hilt like antioxidants and phytonutrients so what could be the problem with an all fruit diet?
Fruitarian diets. What could possibly go wrong?
Like a lot of fad diets, imbalance and lack of variety is the crux of the problem with an all-fruit diet.
For optimal health, the body needs some 50+ nutrients every day in relatively balanced amounts and all fruit diets make that impossible. As well, the word “imbalance” means that there’s too much of one or more things and too little of others.
To put this in perspective, my estimated minimum energy and protein requirements are 2500 calories and 86 g of protein per day based on my height, weight, age & activity level. Because fruit contains fiber, I’ll throw in the 25 to 38 g per day fiber recommendations too, to see how an all fruit diet measures up.
So how much fruit would I have to eat to at least meet my energy requirement which is the most important consideration? Using some of my favourite fruit, the volume of food looks like this:
- 6 bananas: 84 g sugar, 18.6 g fiber, 7.8 g protein
- 9 medium apples: 135 g sugar, 32.4 g fiber, 3.6 g protein
- 3 cups diced mangoes: 69 g sugar, 7.8 g fiber, 4.2 g protein
- 3 ½ cups blueberries: 52 g sugar, 8.4 g fiber, 1.75 g protein
- 8 kiwis: 48 g sugar, 16.8 g fiber, 4.8 g protein
- 1 ½ pears: 26 g sugar, 4.7 g fiber, 1.2 g protein
- 2 ½ oranges: 12 g sugar, 7.8 b fiber, 1.2 g protein
This provides a whopping 426 g (101 teaspoons or 2.1 cups) of sugar and 97 g of fiber but only 25 g of protein
This diet plan would give me enough energy but leave me short about 61 g of protein per day, and what protein it does provide wouldn’t have any meaningful amounts of the essential amino acids my body needs, not the least of which is the all-important amino acid leucine which is crucial for muscle protein syntheses.
Don’t get me started on the gut wrenching amount of fiber; 2 ½ times the upper recommended daily amount. Granted, there are some cultures whose diets provide more than the upper recommended intake and yes the gastrointestinal tract can adapt to higher amounts of fiber BUT this amount would give the bravest of fiber eaters a run for their money. (#bloated, #cramps, #gas)
Eating like this would also leave the most adherent follower short on several minerals like iron, zinc, calcium, sodium, selenium, and vitamins such as D, B12, A (not to be confused with alpha/beta-carotene; they’re not the same thing), E and several B vitamins, as well as, the long chain omega-3 fats EPA, DPA and DHA.
Before anyone says ‘but it’s all natural sugar and the fiber will help to blunt some its impact on blood sugar levels”, y’all need to step back. Natural or not, over 2 cups of sugar is a crap load of sugar with metabolic consequences.
The amount of fructose in an all-fruit diet is the scariest part; some 200 to 300 g per day depending of the amount of calories someone needs – more calories needed means more fruit consumed. My example about would provide about 300 g of fructose per day. So what’s the big deal?
Fructose and health
High intakes of fructose is known to be unhealthy. There is research that shows that excess fructose is only a problem if some is eating too many calories for their needs; that if other sugars are reduced to make room for the fructose, the excess fructose isn’t a problem (1, 2).
It’s important to note that when it comes to discussions about the negative impact of fructose on health, we talk about an upper threshold of 60 g per day, or expressed as an amount of the daily total energy consumed – 40% of calories coming from fructose is considered problematic (3, 4, 5, 6, 7).
Researchers feed this amount to see what the negative effects (8, 9, 10, 11) will be – 40% of my estimated 2500 calories coming from fructose = 250 g. Yup, right up there with what I’d get with an all fruit diet.
Please, not another bite
The other consideration is that this volume of food would be difficult to eat; this is why whole foods like whole grains, nuts, seeds, fruits and vegetables are associated with lower body weight because they are ‘self-limiting’ – it tends to be difficult to over eat whole foods like fruits and vegetables. The table below attempts to spread out the fruit consumption needed to meet my 2500 calories per day in a way that won’t leave me positively stuffed – I can assure you, I wouldn’t be able to do it.
| Meal | Food portion |
| Breakfast |
1 banana 2 apples 1 cup diced mango ½ orange 1 kiwi |
| a.m. snack |
1 banana 1 apple 1.5 cups blueberries 1 kiwi |
| Lunch |
1 banana 2 apples 1 cup diced mango 1 kiwi |
| Early afternoon snack |
1 banana 1 apple 1 cup blueberries 1 kiwi |
| Late afternoon snack |
1.5 pears 1 orange 1 kiwi |
| Dinner |
1 banana 2 apples 1 cup diced mango 1 kiwi |
| Evening snack |
1 banana 1 apple 1 cup blueberries 1 orange 2 kiwis |
This kind of bulk would be especially problematic for athletes and other highly active people. This is why those involved in high volume training often struggle to meet their energy requirements with food and will often need to rely on liquid calories like fruit juice, carbohydrate replacement beverages or even dried fruit to get the calories they need.
Regardless of it shows up, a diet such as this is still a fad. Humans thrive best on a diet based on a variety foods using a variety of preparation methods including both cooked and raw foods.
Doug Cook RDN is a Toronto based integrative and functional nutritionist and dietitian with a focus on digestive, gut, mental health. Follow me on Facebook, Instagram and Twitter.