We’ve discussed the many helpful ways you can use AI to improve your life
One that’s been a game changer for me is using ChatGPT as my nutrition coach.
Coach ChatGPT recently guided me through a successful five-pound cut. It adjusted my macros each week and gave me food suggestions on the fly. It was super handy.
If you’re looking to lose some weight, put on some pounds, or change your body composition (more muscle, less fat), here’s how you can use ChatGPT (or another AI tool) to reach your goals.
Create a Dedicated Chat in ChatGPT That Will Serve as Your Nutrition Coach
Create a dedicated thread within ChatGPT that will serve as your nutrition coach. Name it “Nutrition Coach.” Whenever you have a diet/nutrition-related question to pose or an update to give, you’ll always go directly to this thread instead of creating a new chat.
Using a single thread as your nutrition coach keeps things organized and helps ChatGPT give you smarter and more helpful responses. ChatGPT doesn’t automatically remember what was discussed in another thread (though you can ask it to save things), and unless you explicitly re-provide context or refer to saved notes, it doesn’t know prior details. By keeping all your nutrition-related “journaling” in one chat, ChatGPT will retain the full context — every question you’ve asked, every answer it’s given, and any preferences you’ve shared — allowing it to avoid repeating explanations, build on earlier answers, remember nuances, track your progress, and offer refinements based on where you’ve been and how you’re doing.
When you initially create your chat, you want to prompt ChatGPT to let it know how you want it to act and give answers as your nutrition coach. I got this tip from AI expert Ethan Mollick in my podcast interview with him.
Here’s a prompt you can use:
I want you to act as my personal nutrition coach. I’d like you to be direct, practical, and evidence-based. Base your guidance on the latest research in fat loss, muscle gain, performance nutrition, and behavioral science. Help me stay consistent and make adjustments week to week based on my goals, training, weight, energy, and progress photos. Be concise, honest, and results-focused — no fluff. I’ll be checking in regularly. Treat this like an ongoing coaching relationship.
Upload a Selfie to ChatGPT to Get an Estimate of Your Body Fat Percentage
One of the lessons I got from my conversation with Mollick is to experiment as much as possible with AI to see what it can do because its capacities might surprise you.
Going into my recent effort to shed five pounds, I wanted to use body fat as a way to measure my progress, and I wondered if ChatGPT could estimate body fat percentage based on a picture of myself.
I set up a test to see how accurate ChatGPT’s estimate was by scheduling a DEXA scan. On the morning of my DEXA scan, I snapped a shirtless selfie and told ChatGPT my weight. I then asked it:
Based on my weight of 195 pounds and this picture of me, what would you estimate my body fat percentage to be?
Its answer? 13%.
I then went and got the DEXA scan.
My DEXA scan body fat percentage result? 12.6%.
ChatGPT got its estimate impressively close.
Instead of using complicated or expensive ways to measure body fat, you can just use ChatGPT to gauge it. It’s fast, easy, and pretty accurate.
Once you know your initial body fat percentage, you’ll have a starting point to measure your progress.
Ask ChatGPT to Estimate Your Macro/Calorie Goals
After I got my body fat percentage, I asked my ChatGPT nutrition coach to calculate my macro/calorie goals based on my age, sex, weight, height, activity level, food preferences, and what I wanted to do — lose body fat.
It recommended I consume 2,400–2,500 calories a day and gave me a macro breakdown to follow.
Here’s the prompt I used. Copy and paste it into ChatGPT, changing the details so it matches your situation:
Calculate my calories and give me macro targets based on my goal and these other details about my life and training.
My goal is to lose body fat while maintaining as much muscle as possible. I’m a 42-year-old man. I weigh 195 lbs. I am 6′ tall. My body fat percentage is about 13%. I lift weights 4x per week and do zone 2 cardio 2x per week. I get 10,000 steps daily, but my job is mostly sedentary. I prefer higher protein, moderate carbs, and moderate fat. I eat mostly whole foods like eggs, meat, rice, potatoes, and vegetables.
Please give me daily calorie, protein, carb, and fat targets.
Start Tracking Food and Use ChatGPT to Help
Now that you have your estimated macros/calories, it’s time to put them into use.
Take the macro goals ChatGPT gave you and plug them into your food-tracking app of choice. I’ve been using MyFitnessPal for years. It makes tracking your macros super easy. Their database has over 11 million foods (including foods at most major restaurants) with their corresponding calorie count and macro breakdown. You can even scan the barcode of packaged foods with your smartphone, and their macro information will be entered automatically.
There are other macro-tracking apps out there. Pick one you like because you’ll be more likely to use it.
Once you’ve got an app, there are a few ways Coach ChatGPT can help you track your food and stay on track with your macro goals:
Generate meal prep ideas. If you’re stumped on what to feed yourself so you can hit your macro/calorie goals, ask your ChatGPT nutrition coach for ideas. Here’s a prompt you could use:
Can you help me come up with easy, cost-effective meal prep ideas for breakfast, lunch, and snacks that will help me hit the macro goals you gave me? I want to be able to eat flexibly with my family at dinner, so I’d like these earlier meals to be more controlled and high in protein. Prioritize nutritious, whole foods that are simple to prepare in bulk. I’m okay with eating the same thing every day. Please include estimated calories and macros for each idea. Generate a shopping list based on your ideas.
Estimate macros for home-cooked or restaurant meals. One challenge with tracking is estimating macros for home-cooked meals or items at local restaurants. Now, I snap a pic of the recipe or menu item and ask ChatGPT for a rough macro breakdown. It’s not lab-accurate, but it gets me in the ballpark — which is good enough. I enter the estimate manually into MyFitnessPal.
Suggest meals based on remaining macros. Let’s say your family is making an impromptu stop at Chick-fil-A for dinner. You’ve got 45g protein, 30g carbs, and 20g fat left for the day. Here’s a prompt I’ve used for this scenario:
Here are my remaining macros for the day: ______. What can I get at [insert restaurant] that will fit my macros?
Check in With Your ChatGPT Nutrition Coach
You will check in with your AI coach at the end of each week. You need to do this regularly if you want ChatGPT to be an effective nutrition coach, as it will help you make adjustments based on your progress/setbacks.
Here’s the prompt you’re going to use for your check-ins; also upload a shirtless selfie:
Weight: [X lbs]
Compliance With Macro Goals: [yes/no]
Training: [e.g., 4x/week lifting + 1 HIIT]
Please assess my progress and estimate my current body fat. Be objective and honest. Make adjustments to macros/calories if needed to progress with my fat loss goal.
Coach ChatGPT tweaks my targets based on my results. Over six weeks, I lost about a pound per week, dropping to around 11% body fat, without any guesswork.
Adjust Goals as Desired
Once you’ve accomplished your initial fitness goal with your ChatGPT nutrition coach, feel free to adjust it.
I’ve recently shifted from cutting to maintaining around 191–192 lbs. I asked my ChatGPT nutrition coach what my macros should be for this goal. I’m now eating 2,800 calories daily and trying to recomp — add muscle while staying lean. ChatGPT is helping me manage this transition, too.
Each week, I check in with a photo, weight, and notes on training. If my weight holds steady and I’m still lean, my AI nutrition coach keeps things the same. If my weight jumps too fast or I start looking softer, it reduces calories slightly. It’s pretty dang awesome.
Your On-Demand Nutrition Coach
Could you lose or gain weight without using ChatGPT?
Of course — people have been doing it for centuries.
I lost 30 pounds a few years ago by just gradually reducing my calories. I also did a 15-pound bulk last year. Didn’t use ChatGPT in either situation.
But using ChatGPT has made the process easier, more precise, and more consistent. It’s like having a nutrition coach in your pocket. It gives me solid suggestions, helps me troubleshoot sticking points, and lets me outsource some of the mental load. And, even though I know it’s a bot, the encouragement it offers is affirmative and motivating.
Whether you’re just starting your fitness journey or fine-tuning years of experience in the gym, ChatGPT offers a practical, no-fluff partnership to keep you on track.
