How the Modern Diet Is Driving a Metabolic Crisis
Metabolic Health Series | Issue 02
Last week I wrote in Issue 1 of my Summer Metabolic Health Series, that insulin resistance is at the center of metabolic syndrome. But knowing that insulin resistance exists and understanding how it happens — how a normal, healthy metabolic system gradually loses its footing — are two different things.
This issue is about the how. Specifically, about what in our modern diet is driving this crisis, why certain foods are metabolically far more damaging than others, and what the research actually says about reversing course. The two researchers whose work shapes this conversation most clearly are Robert Lustig and Ben Bikman — and their findings, taken together, reframe what "eating healthy" actually means.
Not All Calories Are Created Equal
For decades, the dominant message in nutrition was simple: calories in, calories out. Eat less, move more. A calorie is a calorie.
This framework has been crumbling under the weight of evidence for years — and nowhere more decisively than in the science of insulin.
Here's the core problem: different foods, even at identical calorie counts, produce profoundly different hormonal responses. And it is those hormonal responses — not the calories themselves — that determine whether your body stores fat or burns it, whether your cells become insulin resistant or remain sensitive to insulin, and whether your metabolism accelerates toward disease or away from it.
At the center of this hormonal story is insulin.
What Insulin Is Actually Doing
Insulin isn't just a blood sugar regulator. It is, as Brigham Young University professor and metabolic researcher Ben Bikman describes it, a master metabolic hormone — one that governs whether the body is in a state of storage or a state of burning.
When insulin is elevated, the body stores. Fat cells grow. Glucose gets shuttled into storage. The liver ramps up fat production. Muscle metabolism is suppressed. When insulin is low, the opposite occurs — the body draws on its stored fuel, burns fat, and operates with metabolic flexibility.
The problem isn't insulin itself. It's chronically elevated insulin — what Bikman calls hyperinsulinemia — which he argues is not merely a byproduct of metabolic disease but one of its primary causes. In his book Why We Get Sick, he makes the case that nearly every major chronic disease — heart disease, type 2 diabetes, fatty liver, Alzheimer's, certain cancers, hormonal disorders — is caused or significantly worsened by persistently high insulin levels.
What raises insulin most? Carbohydrates — particularly refined ones. And among those, one form of sugar stands apart.
The Fructose Problem
Robert Lustig, pediatric endocrinologist and researcher at UCSF, has spent decades building a scientific case against fructose — the sugar found in table sugar, high-fructose corn syrup, fruit juice, and most ultra-processed foods.
His argument isn't that fructose is simply "bad sugar." It's that fructose is metabolized in a fundamentally different way than glucose — and that difference has profound metabolic consequences.
When you eat glucose, it can be used by virtually every cell in the body for energy. When you eat fructose, almost all of it goes directly to the liver, which is the only place it can be processed. The liver then does one of several things with that fructose — and most of them are metabolically problematic:
It converts excess fructose into liver fat (contributing to non-alcoholic fatty liver disease)
It generates triglycerides, which raise cardiovascular risk
It produces uric acid, which contributes to hypertension
It promotes liver insulin resistance — which then drives the pancreas to produce even more insulin
Lustig has described this process as strikingly similar to how alcohol is metabolized. A can of soda and a can of beer — same calories, same destination: the liver, where both create downstream metabolic damage. The difference is that we've never questioned whether children should drink soda.
His research also showed that fructose promotes leptin resistance — a disruption of the hormone that tells your brain you're full. This creates a feedback loop in which fructose consumption drives continued eating, regardless of hunger or caloric need.
The crucial distinction Lustig draws: fructose in whole fruit comes packaged with fiber, which slows absorption and blunts most of these effects. The problem is isolated, concentrated fructose — stripped of fiber and delivered in liquid or ultra-processed form.
The Ultra-Processed Food Machine
Fructose doesn't exist in isolation. It's one ingredient in a broader food category that represents the most significant shift in the human diet over the last 50 years: ultra-processed foods.
Ultra-processed foods — defined as industrial formulations containing ingredients rarely used in home cooking (emulsifiers, flavor enhancers, stabilizers, hydrogenated oils, modified starches) — now account for more than 60% of calories consumed by the average American!
These foods are metabolically disruptive on multiple fronts:
High in refined carbohydrates and added sugars — driving insulin spikes and fructose overload
Stripped of fiber — removing the one dietary component that slows glucose absorption and feeds a healthy gut microbiome
Engineered for overconsumption — combinations of salt, sugar, and fat calibrated to override satiety signals
The result is a food environment in which the default diet keeps insulin chronically elevated, the liver chronically overloaded, and the metabolic system chronically stressed.
The Hidden Sugars You're Probably Not Counting
One of the most common revelations clients have when they start reading labels: sugar is everywhere it shouldn't be.
It appears in bread, pasta sauce, salad dressing, crackers, yogurt, protein bars, flavored nuts, deli meats, condiments, and plant-based milks — often under names designed to obscure its presence: dextrose, maltose, evaporated cane juice, brown rice syrup, agave nectar, fruit juice concentrate.
The American Heart Association recommends no more than 25g of added sugar per day for women and 36g for men. A single flavored yogurt can contain 20–25g. A "healthy" granola bar, 12–18g. A glass of orange juice, 24g. Most people consuming what they consider a reasonable diet are significantly exceeding these thresholds without realizing it.
This matters not because sugar is uniquely toxic in small amounts — it isn't — but because the cumulative, chronic load of added sugar is one of the most powerful drivers of the insulin resistance cascade.
What to Do With This
The research points toward a clear nutritional direction — not a perfect diet, but a coherent framework:
Reduce the insulin burden. The foods that spike insulin most are refined carbohydrates and added sugars, particularly fructose. Reducing these — not eliminating all carbohydrates, but shifting toward whole, fiber-rich sources — is the most direct nutritional intervention for insulin resistance.
Prioritize fiber. Fiber slows digestion, blunts blood sugar spikes, feeds a healthy gut microbiome, and is the single nutrient most consistently associated with metabolic health in the literature. Aim for 30+ grams daily from whole food sources: vegetables, legumes, nuts, seeds, intact whole grains.
Read labels with fresh eyes. Look for added sugar under all its names. If it's in the first five ingredients, or if it appears multiple times under different names, that's a significant source.
Eat food that doesn't need a label. The most metabolically protective dietary pattern is one centered on whole, minimally processed foods — not because of any single nutrient, but because whole foods arrive with their fiber, micronutrients, and satiety signals intact.
Don't fear fat. Fat alone does not spike insulin. The metabolic problems arise when refined carbohydrates and poor-quality fats are consumed together — which is, not coincidentally, the precise formula of most ultra-processed snack foods.
Three Things to Do This Week
Do a sugar audit. Pull out three "healthy" packaged foods from your kitchen and check the added sugar content. You may be surprised.
Swap one refined carbohydrate for a fiber-rich alternative. White rice → cauliflower rice or lentils. Crackers → cucumber or celery. Flavored yogurt → plain full/low-fat yogurt with berries.
Try building your meals around the "blunting" principle — pair any carbohydrate source with protein, fat, and fiber, and notice whether your energy and hunger feel different two hours later.
Next issue: "The Metabolic Health of Midlife Women" — how declining estrogen reshapes insulin sensitivity, why weight gain in your 40s follows different rules, and what Sara Gottfried's research reveals about the cortisol-estrogen-insulin triangle.
This newsletter is educational and does not constitute medical advice.
You now have three things to try this week. But if you've been here before — you know the information isn't usually the missing piece.
If you're ready to stop troubleshooting on your own, let's talk.
A 30-minute discovery call is free, and we'll leave it with a plan that's actually built around your life.
Lisa Marlene Thompson is a Functional Nutritional Therapy Practitioner, somatic facilitator, and health and lifestyle guide for anyone ready to feel more alive in their body. With advanced certifications in menopause science with Dr. Stacy Sims, somatic movement with Michaela Boehm, and sleep and brain health informed by the research of Lisa Mosconi and Matt Walker, her work sits at the intersection of cutting-edge science and deep body wisdom.
Her signature program — Strength, Sleep & Sensuality — is an invitation to come home to your body: to build real strength, reclaim restorative sleep, and rediscover a nervous system that is grounded and provides aliveness in the body that belongs to this chapter of life. She is based in Los Angeles and works with clients worldwide.
Your most vibrant chapter is still ahead.
I'd love to explore what's possible together → Reach out: lisa@lisamarlenethompson.com