Kale, spinach and pear; blueberry, raspberry and blackberry. At first glance, these two popular meal replacement smoothies are everything the doctor ordered.
This healthy image, combined with the fact that (unlike many weight loss foods) they actually taste good, is a key reason for the modern popularity of smoothie diets.
However, knowing your facts can help you decide whether these dietary drinks are really as healthy as they look. Let’s take a look at the premise behind smoothie diets, and then explore some potential red flags.
What is the smoothie diet?
Smoothie diets typically involve replacing most, or even all, meals with fruit and vegetable based drinks. This allows dieters greater control over the pantomime villain of the healthy eating world: calories.
Calories are a measure of the energy content in food and drink, and are also known as kcals. However they’re referred to, we need them - in fact, according to Healthdirect Australia, the average adult requires roughly 2,080 calories a day.
There are several iterations of the smoothie diet. One of the more common options is drinking them in the place of standard meals as a short-term measure. Due to reductions in, notably, carbohydrates and fat, participants can see calorie intake drop to as little as 1,200 per day - resulting in fast weight loss.
Sounds good, right? Well, there are several side-effects of smoothie diets that could lead to health problems.
Potential problems with the smoothie diet
Nutritional deficiencies:
We know what you’re thinking: “Nutritional deficiencies...with a green smoothie? I can’t win”. Firstly, to be clear, a short-term smoothie diet isn’t going to leave you seriously lacking key nutrients.
However, despite what your Gran may have said, you can’t get everything you need from your five-a-day. Over extended periods, smoothie diets can potentially lead to deficiencies in:
- B12 and vitamin D: These nutrients are most commonly obtained from meat or dairy products, so over the longer-term, a smoothie diet may not provide the recommended daily intakes. As with the other items in this list, this problem can be encountered by vegans, and sometimes vegetarians.
- Protein: The majority of protein sources are animal based. Lack of protein on a long term basis has been shown to lead to symptoms such as anaemia.
- Zinc: While you can get zinc from lentils, beans and seeds, humans access it most commonly through meat and shellfish - not common components of a smoothie diet.
Kidney stones
Kidney stones are painful, and potentially dangerous, solid deposits formed in the kidneys - and as many as 80 per cent are made up of calcium-oxalate compounds.
What does this have to do with smoothies? Well, the ‘oxalate’ part of calcium-oxalate refers to an antinutrient that’s found in high concentrations in favourite smoothie ingredients such as spinach, berries and broccoli.
As a waste product, most oxalates leave the body in stool or urine. However, a diet too high in oxalate combined with other risk factors can cause the waste to bind to calcium in the kidney and form crystalline masses.
Too much acid
While fruit is low in carbs and fat, it still contains significant quantities of naturally-occuring acids.
Among the many problems that too much acid can cause is tooth enamel erosion. Indeed, scientific research has shown that certain fruit smoothies caused significant damage to enamel. The worst culprit in this study was the delicious, but highly acidic, mango and passionfruit smoothie.
Thyroid problems
Glucosinolates, commonly found in green smoothie ingredients such as kale, cabbage and sprouts, have been shown by some studies to hinder the ability of the thyroid to absorb iodine.
Iodine is essential to our thyroid gland’s ability to produce hormones. Among other functions, these hormones control our metabolism, and contribute to brain and bone development in infancy.
So, there you have it. The smoothie diet may for some be an effective way of losing weight in the short term - but these drinks perhaps aren’t as innocent as they first appear. As with any major dietary change, if you’re considering trying a smoothie diet, we recommend talking it over with your GP first.
Sources:
https://www.healthdirect.gov.au/kilojoules
https://davyandtracy.com/green-smoothies/why-i-dont-recommend-a-green-smoothie-diet/
https://chriskresser.com/the-dark-side-of-green-smoothies/
https://www.kidney.org/atoz/content/what-are-oxalate-kidney-stones
https://www.kidney.org/atoz/content/calcium-oxalate-stone
https://www.ncbi.nlm.nih.gov/pubmed/24072423
https://www.thyroidfoundation.org.au/Iodine-Deficiency
https://www.betterhealth.vic.gov.au/health/healthyliving/protein
FAQs
In conclusion, smoothies can be a great way to increase intakes of fruit and vegetables in our diet, which would have many health benefits. However, they may contain large amounts of added or natural sugars, which can contribute to dental problems and obesity.
What are 2 potential risks of smoothies? ›
In conclusion, smoothies can be a great way to increase intakes of fruit and vegetables in our diet, which would have many health benefits. However, they may contain large amounts of added or natural sugars, which can contribute to dental problems and obesity.
Is there a downside to smoothies? ›
Smoothies are high in sugar.
Even if they have some added vegetables like spinach or kale, they are still likely to be high in sugar. Watch our animation to learn more about free sugars.
Are smoothie diets safe? ›
Though the diet encourages many nutritious ingredients, it's also restrictive, unsustainable, and very low in calories and protein, increasing the risk of nutritional deficiencies and other side effects. Furthermore, it's not backed by research and is high in carbs and sugar, which might not suit people with diabetes.
What are the disadvantages of green smoothies? ›
Concerningly, green smoothies may also have adverse effects on the thyroid gland. The thyroid gland requires the mineral iodine to produce thyroid hormones. Cruciferous vegetables—common ingredients in green smoothies—contain compounds called glucosinolates, which inhibit iodine uptake by the thyroid.
What are the pros and cons of smoothie? ›
In conclusion, smoothies can be a great way to increase intakes of fruit and vegetables in our diet, which would have many health benefits. However, they may contain large amounts of added or natural sugars, which can contribute to dental problems and obesity.
What are the negatives of blending food? ›
Some blenders produce heat from the blades when they're switched on for prolonged periods, this heat can affect nutrients. Some B vitamins, as well as vitamins C, A, D, E and K, can all be damaged and reduced by heat. It's not just vitamins either, some minerals like potassium and magnesium will also be affected.
Is it safe to drink smoothie everyday? ›
"Drinking smoothies every day can have positive health benefits, like increasing your intake of fruits and vegetables, fiber, and antioxidants," says Lisa Young, PhD, RDN.
Can I drink smoothies every day to lose weight? ›
But are smoothies all they're cracked up to be for shedding pounds? Yes and no. While most weight loss experts don't recommend substituting smoothies for every meal of the day, drinking them here or there (or even daily) can support weight loss goals.
Are smoothies and juices not always healthy? ›
The final verdict is that both juicing and smoothies can be beneficial if done in moderation with a balanced diet. However, smoothies come out on top in terms of nutrients and fiber for weight loss and digestion.
The guidance for the majority of us is to limit our daily intake of smoothies and juices to one glass of 150ml. This contributes a maximum of one of our five-a-day. For a child, a smoothie portion will depend on their age and activity levels.
How to lose 10 pounds in a week? ›
To lose 10 pounds in one week, you'll need to burn between 3,500 and 5,000 calories more than you consume each day by restricting your diet to small portions of nutritious yet low-calorie foods, and significantly increasing your aerobic exercise with interval training, sports, and other vigorous activities.
Is it better to eat fruit or drink a smoothie? ›
Why do I need to watch fruit juices and smoothies but not the whole fruit? Fructose adds to your intake of free (added) sugars. Whole fruit, on the other hand, does not. Whole fruit contains fibre (roughage), vitamins and minerals, which are good for your overall health.
Can smoothies upset your stomach? ›
A while we're on the subject of stomach upset, certain fruits and veggies are so powerful that you may experience some stomach distress if you drink too much of them. Too many leafy greens or wheatgrass can do this. For others, too much beet will do the same.
Do smoothies cause bloating? ›
If you're not used to a high-fiber diet and suddenly you start downing fruit and veggies left and right, your body might have a hard time processing, which will causing excess gas and bloating. Try drinking your smoothie in 8-oz increments, and waiting fifteen minutes or so between cups.
What happens if you drink too much smoothie? ›
Free sugars may lead to dental decay, provide excess calories and cause a rapid rise in blood sugar levels. For these reasons it's best to enjoy your smoothie with other food, ideally at mealtimes, and to limit the number of glasses you consume.
What are the disadvantages of blended juices? ›
Blending cons
Blending smoothies won't cause your blood sugar to spike as much as with drinking juice, but they can increase your blood sugar levels because of all the fruits. To help keep sugar in check, use no more than two servings of fruit per smoothie. Too much fiber can cause problems like gas and indigestion.
Is having two smoothies a day bad? ›
While there are many different smoothie recipes that you can use for weight loss, the general rule of thumb is to incorporate smoothies in place of meals 1 or 2 meals per day. This will help to reduce your overall calorie intake and give your body the nutrients it needs to function properly.
