In our last series, we explored carbs from the inside out—covering refined carbs and cravings, the gut’s role, how cooking changes carb digestion, and how metabolism starts before you eat.
Now, we’re zooming out.
In this new series, we explore the outside-in story with Lourdes Castro, MS, RD, registered dietitian and Director of the NYU Food Lab. She takes us outside the body to examine how processing and refinement affect digestion speed, carb types, fiber’s role, real-world food choices, and carb myths, giving us a practical, food-focused perspective.
Starting with: What actually makes a carb “refined”? Why does processing affect how fast we digest it? And how does that speed shape our energy and blood sugar?
In this opening clip, Castro uses one of the clearest analogies I’ve heard to explain it all: think of carbs as a pearl necklace.
"If you think of a carbohydrate as a pearl necklace... The longer the necklace, the more complicated the carbohydrate is."
And your body? Imagine it as a donut. Yes, a donut! We're essentially hollow, with a tube running from our mouth to our... well, the other end. Everything we eat travels down this tube, which is actually outside our circulatory system. The goal of digestion? To break down food into tiny molecules that are small enough to pass from that donut hole (your digestive tract) into the donut itself (your body).
Castro further explains how processing affects this: "Processing is like polishing the pearls—it makes them easier and faster to digest."
Highlights from the Clip:
Carbs = pearl necklaces → your body clips them into individual “beads” to absorb
Simple carbs = short strands = fast digestion, quick energy spike
Complex carbs = long strands = slower digestion, steadier release
Refining is like polishing a pearl → it digests faster, but that’s not always better
Your digestive tract is like a donut hole → food isn’t “in” your body until it’s absorbed
Takeaway: Choose Your Pearls Wisely
The more we process a carb, the faster it moves through us, and the more dramatic the effect. Whole, unrefined carbs force your body to work a little harder (and that’s a good thing).
This is part of my ongoing series on Carbs & Metabolic Health, where I talk with leading researchers to cut through diet dogma and bring you real science, simply explained.
🔜 Coming Tuesday: The Three Types of Carbs & Fiber's Unique Role (Soluble vs. Insoluble)
Read the article behind the interview: How to Make Carbs Healthy Again
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