HeraSphere #19: The science behind holiday weight gain

Hi friends,

Let's talk about something that's probably already on your mind as the holidays approach: weight gain. I recently overheard a friend say “I feel like I just look at food and gain weight these days!” How many of us are in the same boat? For the holidays, I'm not going to tell you to skip the stuffing or do extra burpees. Instead, I want to share what's actually happening in your body and why understanding the science makes all the difference.

Holiday weight gain is actually more about hormones than about willpower.

The TL;DR

• Insulin determines whether you store fat or burn it. When insulin is high (from sugar, constant snacking, or stress), fat gets locked in your cells and can't be released.

• Leptin is another key hormone: When leptin signaling is disrupted (from poor sleep, chronic dieting, or inflammation), your brain thinks you're starving and hoards fat—even when you're not.

• Exercise matters far less than what you eat. When you diet and exercise without strength training, up to half of what you lose is muscle. Then when you regain weight (and you will, because severe restriction crashes leptin), 80% of what comes back is fat. More spin classes alone won't fix this. Building muscle and adjusting what's on your plate will.

• Healthy fats don't make you fat. Avocados, nuts, and olive oil actually improve insulin sensitivity, keep blood sugar stable, and help you stay full—so you eat less overall.

• The holiday game plan: Eat protein at breakfast. When you sit down to the big meal, eat veggies first, protein second, carbs last (this cuts glucose spikes by 75%). Take a 10-minute walk after eating. Protect your sleep like it's sacred. And if you're drinking, stick to dry wine or clear spirits—skip the sugary cocktails.

• The bottom line: Restriction backfires. Hormone stability wins every time.

How Weight Gain Actually Works

At the most basic level, when you consistently eat more energy than you use, the excess gets stored as fat. But it is more than calories in vs calories out. That is oversimplifying the process and creates misleading behaviors. Your body converts extra calories into triglycerides and tucks them inside fat cells. The hormone insulin is the key player here—when it's high, your body is in storage mode. Fat burning? Turned off.

Over time, fat cells enlarge and new ones can form—which is why weight regain becomes easier the more times we've gained and lost. This isn't a character flaw. It's physiology.

Why What You Eat Matters More Than How Much

All calories are not handled the same way:

• Fat stores most easily—minimal conversion needed

• Carbs spike insulin; once glycogen is full, the rest becomes fat

• Protein is hardest to store as fat and keeps you fullest longest

This is why a high-protein, fiber-rich meal feels completely different than grazing on crackers and cheese all afternoon. Same calories, wildly different hormonal response.

How Fast Does Sugar Turn Into Fat?

Here's what happens when you eat that holiday pie: Within 15-30 minutes, simple sugars hit your bloodstream, and your blood glucose peaks around 30-45 minutes after eating. Your pancreas immediately releases insulin to shuttle that glucose into cells for energy.

Your body can maintain blood glucose levels for about 3-4 hours. Any glucose not immediately used gets stored as glycogen in your liver and muscles—but here's the catch: you can only store about 500-600 grams of glycogen total. Once those tanks are full, any excess glucose starts converting to fat through a process called lipogenesis.

The timeline: Within 4-8 hours after a meal, your body begins storing excess calories as fat. Simple sugars convert faster because they're absorbed so quickly. Complex carbs take longer to digest, giving your body more time to use the energy before it gets stored.

This is why eating a slice of pie after a huge meal (when glycogen stores are already full) goes straight to storage—while the same slice after a morning workout might get burned for fuel.

Insulin: Your Fat Storage Switch

Think of insulin as a traffic cop directing energy. When blood sugar rises, your pancreas releases insulin to move glucose out of your blood and into cells. Insulin tells your liver to stop releasing stored glucose. It tells your fat cells to absorb and store fat. And critically—it tells your body to STOP burning stored fat for energy.

When insulin is chronically elevated (from constant snacking, high-sugar diets, or insulin resistance), your fat cells become like a one-way door: fat goes in easily, but can't get out. This is what Dr. Vonda Wright calls the "fat lock" problem—you have plenty of stored energy, but your body can't access it.

Signs of insulin resistance:

• Afternoon energy crashes

• Intense carb cravings (especially after eating carbs)

• Belly fat accumulation

• Feeling tired AND hungry at the same time

This is physiology, not failure.

Leptin: Your "I'm Fed" Signal

Leptin is produced by your fat cells and tells your brain you have enough stored energy. When it's working well, hunger stays stable, metabolism runs normally, and your body feels safe.

But here's where it gets tricky: You can't just "eat more leptin"—no foods contain it. Leptin levels are directly tied to how much body fat you have. The real issue for most women isn't low leptin—it's leptin resistance, where your brain can't "hear" the signal even when leptin is present.

What Supports Healthy Leptin Function

While you can't directly boost leptin through food, you can improve how well your body responds to it:

• Prioritize sleep. Studies show sleep-deprived people have up to 15% lower leptin and higher ghrelin (the hunger hormone). One bad night can make you significantly hungrier the next day.

• Lower triglycerides. High triglycerides can block leptin from crossing the blood-brain barrier. Foods that help: fatty fish, berries, leafy greens, legumes, and whole grains.

• Eat enough protein. Higher-protein meals elevate post-meal satiety hormones including leptin sensitivity. Aim for 1.0-1.2g per kg of body weight.

• Reduce inflammation. Chronic inflammation disrupts leptin receptors. Cut highly processed foods and add anti-inflammatory omega-3s.

• Don't chronically under-eat. Severe calorie restriction tanks leptin, triggering your brain's starvation response—more hunger, slower metabolism, weight regain.

The Hard Truth: You Can't Out-Exercise a Bad Diet

I know this isn't what we want to hear, but the research is clear: what you eat has a far greater impact on weight than how much you exercise. Here's why.

When you just calorie restrict and exercise without resistance training, studies show you lose 25-50% of your weight as muscle. Muscle is your metabolic engine—it's where your mitochondria turn glucose into energy. Lose muscle, and your body becomes less efficient at processing what you eat.

Then when you regain weight (which happens when leptin crashes from restriction), 80% of what you gain back is fat. This is the yo-yo cycle that makes each round of weight loss harder than the last.

The solution isn't more cardio—it's body recomposition: building or maintaining muscle while losing fat. Strength training 2-3x per week preserves your metabolic engine.

A strategic 10-minute walk after meals can lower glucose more effectively than an extra hour at the gym. It's not that the 10-minute walk burns more calories than an hour of exercise—it doesn't. It's that the timing makes it dramatically more effective at preventing the glucose spike that triggers fat storage. The hour at the gym is great for fitness, muscle building, and overall health. But for blood sugar control after a big holiday meal, the short walk wins.

Why Healthy Fats Don't Make You Fat

This might seem counterintuitive: if fat stores most easily, why would eating avocados and nuts help with weight? The answer lies in insulin response and satiety.

Unlike carbohydrates, healthy fats don't spike insulin. When you eat an avocado or a handful of almonds, your blood sugar stays stable, insulin stays low, and your body stays in a state where it CAN access stored fat for energy. A meta-analysis of feeding trials found that replacing carbohydrates with unsaturated fats (like those in nuts, olive oil, and avocados) improved insulin sensitivity and glucose control.

Here's the key difference:

• Monounsaturated fats (avocados, olive oil, almonds) actually INCREASE insulin sensitivity

• Omega-3 polyunsaturated fats (fatty fish, walnuts, flaxseed) reduce inflammation and lower triglycerides

• Saturated fats (from processed foods, red meat) can promote insulin resistance when consumed in excess

Plus, healthy fats keep you full. A meal without fat won't satisfy you, leading to more snacking and more insulin spikes throughout the day. Including a serving of healthy fat at each meal—some avocado, a drizzle of olive oil, a handful of nuts—helps regulate your hormones and actually makes weight management easier.

Why Midlife Feels Different

If you're 40+, you're navigating a perfect storm:

• Lower estrogen = reduced insulin sensitivity

• Higher stress load = more cortisol (which blunts leptin signaling)

• Sleep disruptions = unstable hunger hormones

• Skipping meals = lower leptin, triggering starvation response

Midlife weight changes aren't a failure of discipline. They're a shift in physiology that requires a different approach.

Holiday Strategies That Actually Work

Instead of restriction (which backfires by tanking leptin), focus on keeping your hormones stable.

Eat protein and fiber before: Eat 20-30g protein at breakfast (eggs, Greek yogurt, or a protein smoothie). Have a fiber-rich snack before events—apple + nut butter or veggies + hummus

Sequence your meal: Eat veggies first, then protein, then carbs last. This simple order reduces glucose spikes by up to 75%. The fiber creates a protective coating in your gut that slows sugar absorption. Pick your carbs intentionally—choose what's truly special, skip the fillers.

Take a 10-minute walk after big meals. It lowers glucose more effectively than willpower ever could.

Protect your bedtime. Poor sleep the night before a holiday meal increases calorie intake the next day by 20-30%, drops leptin by 15%, and spikes ghrelin (your hunger hormone).

The Alcohol Question

Alcohol lowers inhibitions and raises insulin—so choosing smarter options matters.

Best choices (lowest insulin impact):

• Clear spirits (vodka, tequila, gin) with club soda + citrus

• Brut champagne or sparkling wine

Skip (highest spikes): sweet cocktails, dessert wines, anything with juice or syrups.

Smart moves: Always eat before drinking (protein + fiber is ideal). Pair drinks with protein or fat, not carbs. Alternate every drink with sparkling water. Stop 3+ hours before bed—alcohol disrupts REM sleep and increases next-day cravings.

The Bottom Line

Holiday weight gain is biological, not moral. When you stabilize leptin, insulin, sleep, and stress, your metabolism can become far more predictable—even during the most indulgent season of the year.

Focus on hormone stability over restriction. Eat enough protein and healthy fats. Protect your sleep. Move your body—but know that what's on your plate matters more than hours on the treadmill.

Here's to enjoying the holidays and feeling good in your body.

Wishing you and your family a wonderful Thanksgiving!

Lilly

P.S. Drop me a note about your favorite holiday survival strategies - I’d love to learn your tips and tricks too!