Green Protein Smoothie

What this is

A blended drink with real protein and actual greens in it, made in two minutes.

Smoothies attract more nonsense per calorie than almost any other food. This one is built around two questions somebody has genuinely tested: whether protein before training causes gut problems, and whether the greens do anything measurable.

One of those answers is more encouraging than the other.

Ingredients

For 1 large smoothie

1 scoop whey protein, about 30 g, vanilla or unflavoured 2 large handfuls spinach, about 60 g 1 banana, ideally frozen 150 g frozen berries or half a frozen mango 1 tbsp nut butter or 15 g oats 250 ml milk or water 1 tsp cinnamon Juice of half a lime, which cuts the green flavour more effectively than anything else

Optional: a few mint leaves, a thumb of ginger, ice

Method

1. Liquid in the blender first. This is not fussiness, it stops the powder welding itself to the base.

2. Add the spinach and blend on its own for 20 seconds until the liquid is uniformly green with no visible leaf. Doing this before the frozen items go in is the difference between smooth and stringy.

3. Add the protein, banana, berries, nut butter and cinnamon.

4. Blend 45 seconds until completely smooth.

5. Add the lime juice and pulse once.

6. Drink it. It separates within about ten minutes, which is normal and not a defect.

The protein-before-training question

This study exists because of a habit, and the habit turned out to be untested.

Exercise-induced gastrointestinal symptoms affect a significant portion of endurance runners, and research on what runners eat before training shows many of them avoid high-protein foods specifically to manage those symptoms. Clinical trials evaluating whether that strategy works were lacking.

So thirteen recreational runners, eight women and five men, completed a 10 km treadmill run at 85 percent of their own 10 km race pace in a single-blind crossover design. Sixty minutes before running, they drank a shake with carbohydrate and whey protein at either a low dose of 0.15 g per kg of body mass or a moderate dose of 0.4 g per kg. The study quantified gastrointestinal symptoms, gut fullness, blood glucose response and ratings of perceived exertion.

The title states the result: whey protein intakes up to 0.4 g per kg body mass are well tolerated before a 10 km run at 85 percent of race pace.

For an 80 kg person, 0.4 g per kg is 32 g of whey, which is roughly one scoop. An hour before a hard 10 km.

If you have been avoiding protein before training because you assumed it would sit badly, this is the trial that examined the assumption directly.

Thirteen recreational runners in a single crossover study of one exercise mode. It is small, and it does not speak to heavier resistance sessions or to individuals who already know a shake sits badly for them.

What the spinach is actually for

Leafy greens carry inorganic nitrate, which the body converts along a pathway ending in nitric oxide, and nitric oxide affects blood flow and muscle contractility. That is the mechanism behind every beetroot juice claim you have ever seen.

A systematic review and meta-analysis assessed the acute effects of nitrate supplementation on muscle strength, power and sprint performance specifically in healthy females, searching PubMed, Web of Science, Scopus, SPORTDiscus and Cochrane CENTRAL from inception to July 2025. It included randomised controlled trials of oral inorganic nitrate, from beetroot juice or nitrate salts, against placebo in women aged 18 to 30, with outcomes covering maximal voluntary contraction, countermovement jump height, peak power and sprint measures. Studies not reporting sex-specific results were excluded.

That exclusion criterion is why this review needed to exist. Most nitrate studies have focused on males, and the effects in females during high-intensity short-duration exercise remain unclear.

That is a straightforward statement of an evidence gap, and it is the reason I am not going to tell you the spinach in this smoothie improves your sprints.

What the greens are reliably doing here is adding volume, fibre and micronutrients for very few calories, while being completely invisible behind banana and lime. That is enough.

What nitrate does not appear to do

There is a second nitrate claim in circulation that deserves shutting down.

A PRISMA 2020 systematic review and meta-analysis searched PubMed, Scopus, Web of Science and Embase to April 2026 for randomised controlled trials of nitrate supplementation in adults with obesity, examining body weight, BMI, blood pressure and lipid markers. Eight trials with 199 participants were pooled.

No significant effects were observed on body weight, BMI, or diastolic blood pressure.

A statistically significant reduction was found in systolic blood pressure, with a standardised mean difference of negative 0.32, a confidence interval running from negative 0.63 to negative 0.01, and a p value of 0.04.

Look at that confidence interval. The upper bound is negative 0.01, meaning the effect only just clears zero. It is significant by the conventional threshold and it is not large.

So: no weight or BMI effect from nitrate, and a small blood pressure signal from eight trials totalling 199 people.

Drink this because it is a fast way to get protein, fruit and greens into you. Not because the spinach is doing something to your body composition.

This meta-analysis studied adults with obesity taking nitrate supplements, which is a different population and a different exposure from spinach in a smoothie.

Storage and swaps

Drink it fresh. It separates fast and the texture goes within the hour, though shaking it back together is fine.

You can freeze the solid ingredients in bags portioned out, then tip a bag into the blender with liquid and protein. This is the single change that makes people actually keep doing it.

Swap spinach for kale, though kale needs longer blending and more lime.

Swap whey for a plant protein blend. The texture is grittier and it needs more liquid.

Drop the banana and add half an avocado if you want it less sweet. It goes thicker and the greens come forward.

And blend the greens with the liquid first, alone, before anything else goes in. It is the only technique in this recipe and it is the one people skip.