Milks & Impact on Insulin Levels

For anyone on your programme with insulin resistance concerns, unsweetened almond milk is the safest daily choice. Oat milk should be treated essentially as a grain-based sugary drink — which is precisely what it is once the manufacturing enzymes have done their work.

🚨 Oat Milk — the worst offender

Your friend’s claim doesn’t hold up. Oat milk contains a type of sugar called maltose, which has a glycemic index of 105 — even higher than pure glucose. When oats are processed to create oat milk, enzymes are added to break down the oat starch, causing complex carbs to be converted into quickly digestible simple carbs. [Study 1, Study 4]

A published review in PMC (National Institutes of Health) found that oat proteins stimulate the release of insulin, and that the increased insulin response was in accordance with the pattern of GIP and GLP-1 release — the very hormones that signal the pancreas to produce insulin. [Study 1]

To put this in practical context, oat milk has the highest glycemic index among popular alternatives at approximately 69 — significantly higher than dairy milk or most other plant milks. If you use oat milk daily in coffee and other beverages, you could be consuming 40–60g of high-GI carbohydrates from milk alone. [Study 2, Study 3]

A real-world CGM (continuous glucose monitor) test confirmed this: one user drank coffee with oat milk on an empty stomach and her blood sugar spiked to 123 mg/dL, compared to peaking at just 74 mg/dL when she drank the same coffee black. [Study 3]

🐄 Cow’s Milk — low GI but an insulin paradox

Cow’s milk is more nuanced. A low GI was observed in all dairy products, ranging from 37 to 51. [Study 2, Study 6] The fat and protein content slow gastric emptying, which blunts the glucose response.

However — and this is important for your work, John — dairy has what’s known as an insulin index paradox: dairy milk has an unusually high insulin index relative to its glycemic index, meaning it triggers more insulin than you would expect based on its blood sugar impact alone. Research published in Diabetes Care showed that the combination of dairy protein and lactose produced an insulin response 3–4 times higher than would be predicted by the glycemic index. [Study 2]

For most people this is beneficial (it clears glucose efficiently), but for someone with existing hyperinsulinemia or insulin resistance, it is worth being aware of.

🌰 Almond Milk — the best option for insulin

Unsweetened almond milk is the clear winner here. The glycemic index of almond milk is approximately 25–30, classifying it as a low GI food with a glycemic load of just 3.9. [Study 6]

A randomised controlled trial from the Joslin Diabetes Center in Boston found that carbohydrate-matched cow’s milk elicited a significantly greater insulin and glucagon response compared to almond milk — making unsweetened almond milk the superior choice for anyone managing insulin sensitivity. [Study 5] The key word, though, is unsweetened — sweetened versions can behave very differently.

🥥 Coconut Milk — surprisingly problematic

Coconut milk is often assumed to be safe on low-carb diets because of its fat content, but the research on the carton-style coconut drink (as opposed to tinned coconut cream) is concerning. A PMC study screening 17 commercial plant-based milks found that coconut- and rice-based milk drinks had GI values exceeding 96, driven by high glucose and maltose content from processing. [Study 6] Tinned full-fat coconut cream is a very different product — it is very low carb — but the watered-down coconut drink sold as a milk alternative is not the same thing.

Research Studies

 
Study 1
Title: Oat-Based Foods: Chemical Constituents, Glycemic Index, and the Effect of Processing
Date: 2021
Source: Foods (MDPI), published via PubMed Central (PMC)
URL: https://pmc.ncbi.nlm.nih.gov/articles/PMC8229445/
Summary: This review examined how the chemical composition of oats — including starch, beta-glucans, proteins, and phenolics — influences glycemic index across different oat products. It found that oat proteins stimulate insulin release through incretin hormone pathways (GIP and GLP-1). It also confirmed that processing methods such as milling significantly raise the GI by breaking down the protective oat matrix.

Study 2
Title: Glycemic Responses of Milk and Plant-Based Drinks: Food Matrix Effects
Date: 2023
Source: Nutrients, published via PubMed Central (PMC)
URL: https://pmc.ncbi.nlm.nih.gov/articles/PMC9914410/
Summary: This comprehensive review compared the glycemic and insulinemic responses of dairy milk and plant-based alternatives, analysing how food matrix factors such as fat, protein, and carbohydrate type affect glucose absorption. It found dairy milk had the lowest GI (47), while coconut and rice drinks reached GI values up to 100. It concluded that for plant-based drinks, compositional differences can lead to significantly stronger glycemic responses than dairy.

Study 3
Title: Impact of Oat Processing on Glycaemic and Insulinaemic Responses in Healthy Humans: A Randomised Clinical Trial
Date: 2019
Source: British Journal of Nutrition (Cambridge University Press)
URL: https://www.cambridge.org/core/journals/british-journal-of-nutrition/article/impact-of-oat-processing-on-glycaemic-and-insulinaemic-responses-in-healthy-humans-a-randomised-clinical-trial/B81334B99F41D96F854D3986D4178592
Summary: This randomised clinical trial directly measured blood glucose and insulin responses in healthy humans after consuming differently processed oat products. It found that more heavily processed oats (thinner/instant varieties, closer to what is used in oat milk) produced insulin responses comparable to refined grain controls. It highlighted that disrupting the integrity of the oat kernel removes the metabolic protection offered by intact oats.

Study 4
Title: A Systematic Review and Meta-Analysis of Randomized Controlled Trials on the Effects of Oats and Oat Processing on Postprandial Blood Glucose and Insulin Responses
Date: 2021
Source: The Journal of Nutrition (Oxford Academic / ScienceDirect)
URL: https://www.sciencedirect.com/science/article/pii/S002231662200044X
Summary: This meta-analysis pooled data from multiple randomised controlled trials to assess how oat processing affects post-meal glucose and insulin. It found that intact oat kernels and thick oats significantly reduced both glycemic and insulin responses compared to refined grain controls, while thin/instant/quick oats showed no significant benefit. The authors concluded that fine processing — the type used in commercial oat milk production — eliminates the glycemic advantage of oats.

Study 5
Title: Effect of Almond Milk Versus Cow Milk on Postprandial Glycemia, Lipidemia, and Gastrointestinal Hormones in Patients with Overweight or Obesity and Type 2 Diabetes: A Randomized Controlled Clinical Trial
Date: 2024
Source: Nutrients, published via PubMed Central (PMC) — Joslin Diabetes Center, Boston
URL: https://pmc.ncbi.nlm.nih.gov/articles/PMC12251527/
Summary: This crossover RCT from the prestigious Joslin Diabetes Center compared almond milk directly against cow’s milk in 22 patients with Type 2 diabetes and obesity. It found that carbohydrate-matched cow’s milk elicited a significantly greater insulin and glucagon response than almond milk. The authors concluded that almond milk produced lower postprandial insulin demand, though they called for further investigation into the long-term implications.

Study 6
Title: Evaluation of Physicochemical and Glycaemic Properties of Commercial Plant-Based Milk Substitutes
Date: 2017
Source: Nutrients, published via PubMed Central (PMC)
URL: https://pmc.ncbi.nlm.nih.gov/articles/PMC5325842/
Summary: This study screened 17 commercial plant-based milk alternatives, measuring their GI using in-vitro methods alongside a bovine milk control. It found that coconut and rice-based drinks had GI values exceeding 96, explained by their high glucose and maltose content from processing. Bovine milk scored the lowest GI at 47, followed by select soy, almond, cashew, and macadamia milks in the low GI range.