What to Expect During the First Week of a Low Carb Diet

28 November 2025

Thinking about going low carb? Or maybe you’ve already taken the plunge, and now you're wondering what's going on with your body. You’re not alone! The first week of a low carb diet can be a rollercoaster, both physically and emotionally. But don’t worry—I’ve got you covered.

This guide will walk you through exactly what to expect during that crucial first week. We’re talking cravings, energy crashes, weird breath (yes, that’s a thing), and of course, the major benefits that’ll make you want to stick with it.

Let’s cut the carbs (pun intended) and dive in.

What Is a Low Carb Diet Anyway?

Before we get into the nitty-gritty of week one, let’s just clarify what “low carb” really means.

A low carb diet is exactly what it sounds like: you're cutting way back on carbohydrates—think bread, pasta, rice, sugary drinks—and instead loading up on protein, healthy fats, and veggies. There are a few different versions of it (like keto, Atkins, and paleo), but they all follow the same basic principle: fewer carbs = more fat-burning.

The goal? To shift your body from burning sugar (glucose) for energy to burning fat. This process is called ketosis, and it’s kind of like flipping a metabolic switch in your body.

Sounds intense? It can be, especially in that first week. But don’t panic. It’s all part of the process.

Day 1-2: The Excitement (and Denial) Phase

You cleaned out your pantry. You stocked up on eggs, avocados, and cauliflower everything. You’re feeling pumped. Day 1 of your low carb journey starts with scrambled eggs and bacon—what’s not to love?

What You're Likely Feeling:

- Motivated. You’re ready to crush this.
- Full but craving. Even if you’re not hungry, your brain might scream for bread or sugar out of habit.

Remember, your body is still running on glucose at this point. It hasn’t noticed the carb shortage just yet.

Pro Tips:

- Drink lots of water. Carbs hold onto water in your body. Cut them out and you’ll lose water fast.
- Salt your food. You’ll be flushing out sodium too, and this can lead to headaches or fatigue if you’re not careful.

Day 3-4: Hello, Carb Withdrawal

This is where things get... real.

Your body realizes there’s no sugar coming in, and it starts to freak out a little. This phase is lovingly known as the “keto flu” (even if you’re not doing full-on keto).

Common Symptoms Include:

- Headaches
- Brain fog
- Fatigue
- Mood swings
- Nausea
- Muscle cramps
- Difficulty sleeping

Sounds brutal, right? It can be. But hang tight—this is temporary.

Why It Happens:

Your body is scrambling to adjust to a new fuel source. It’s like trying to run your car on vegetable oil. It works eventually, but the engine has to adapt.

You’re also losing electrolytes and water, which can throw your system out of whack.

What to Do:

- Hydrate like it’s your job. Think 2-3 liters per day.
- Replenish electrolytes. Add magnesium, potassium, and sodium to your diet—through salt, leafy greens, bone broth, or supplements.
- Don’t be a hero. Take naps, rest more, and avoid intense workouts for a few days.

This too shall pass!

Day 5-6: Turning the Corner

You’re over the hump. Your cravings aren’t nearly as strong, and guess what? You might actually be feeling... good.

Signs You're Adapting:

- Increased mental clarity
- More consistent energy levels
- Reduced appetite
- Fewer cravings for sugar and carbs
- Slight weight loss (mostly water weight at this point)

Your body is starting to use fat as fuel. That sluggish, foggy feeling from earlier in the week starts to lift. You might even notice your jeans feeling a bit looser. Victory!

Keep Doing This:

- Eat enough fat and protein! If you’re hungry, EAT.
- Keep carbs super low—under 20-50 grams for most low-carb diets.
- Watch your fiber intake—too little can cause digestive issues.

Day 7: A New Normal?

Congratulations—you made it through the first week! It’s not all sunshine and six-pack abs just yet, but you’re definitely on your way.

By Day 7, most people:
- Feel more mentally alert
- Have better control over hunger
- Notice increased energy (especially in the morning)
- Experience digestive changes (yes, we’re talking about bathroom habits)
- Might have dropped 2 to 10 pounds (mostly water, but still!)

Cravings Still Lurking?

That’s normal. Especially if you were a sugar fiend (no judgment). It might take a few more weeks for that to fully go away. But the longer you stay low carb, the easier it gets.

Possible Side Effects During the First Week

Let’s keep it real. The first week of a low carb diet isn’t all roses. Here are a few things that might pop up—and how you can deal:

1. Bad Breath

Yup, your breath might smell like nail polish remover. This is due to acetone, one of the ketones your body produces in ketosis. It’s harmless, but annoying.

Fix it: Chew sugar-free gum or mints, brush often, and drink lots of water.

2. Constipation

Less fiber + water loss = bathroom blues.

Fix it: Eat fibrous veggies (like broccoli and spinach), drink more water, and consider magnesium supplements.

3. Insomnia

Some people report trouble sleeping when they first go low carb.

Fix it: Eat a small meal with healthy fat before bed, and avoid caffeine after noon.

Mental Shifts: Low Carb Isn’t Just Physical

Changing your eating habits isn’t just about what you put on your plate—it’s a whole mindset shift.

You may start questioning your relationship with food. You’ll probably realize just how often you used carbs for comfort or out of habit. And you’ll notice how different your hunger cues become when your blood sugar isn’t spiking and crashing all day.

This awareness is powerful. Use it.

Tips to Make Your First Week Easier

Let’s be real—starting a low carb diet isn’t easy. But it becomes a lot more manageable with the right strategies.

1. Meal Prep Like a Boss

The last thing you want is to be hangry and surrounded by carbs. Prep your meals ahead of time—think grilled chicken, sautéed veggies, egg muffins, avocado tuna salad.

2. Read Labels

Sugar is sneaky. It’s hiding in sauces, dressings, even "healthy" snacks. Always check the nutrition label, and aim for foods with less than 5g of carbs per serving.

3. Get Support

Join a Facebook group, follow low carb influencers, or rope in a buddy. Having someone to vent (and share recipes) with makes a big difference.

4. Focus on the Long Game

You’re not just trying to drop 5 pounds for the weekend. You’re shifting your body and lifestyle. That takes time. Be patient and stay the course.

FAQs About the First Week on a Low Carb Diet

Q: How much weight will I lose in the first week?
A: Most people lose 2-10 pounds in the first week. But remember, much of that is water weight. Fat loss takes longer.

Q: Is it safe to feel this tired and foggy?
A: Yep, it’s totally normal. Your body is adapting. If you feel extremely unwell, it’s worth checking in with your doctor.

Q: Can I drink alcohol?
A: In moderation. Dry wines and clear spirits like vodka and tequila have fewer carbs. Skip the beer and sugary mixers.

Q: Is it okay to “cheat” during week one?
A: Honestly? Try not to. The first week is the hardest for a reason. If you cheat, you might reset your progress and feel worse.

Final Thoughts

Week one on a low carb diet is a wild ride. There’s excitement, withdrawal, cravings, and eventually—clarity. Your body is learning to run on a brand-new fuel source, and that takes some serious adjusting.

But once you get through those first shaky days, things get easier. The cravings fade. Your energy stabilizes. And you start feeling like the best version of yourself again.

So hang in there. Go easy on yourself. Celebrate the small wins. And trust the process—because big changes are happening, even if you can’t see them yet.

You’ve got this!