Why the Same Diet Can Work for One Person and Fail Another: The Rise of Personalized Nutrition

There is a question I hear quite often: “Ryan, I followed the same diet as my friend. It worked brilliantly for them. Why didn't it work for me?” 

And sometimes the person has genuinely done everything they were told to do.

• They reduced their calories.

• They cut down on sugar.

• They increased their protein.

• They started exercising.

• They followed the meal plan consistently.

But the results were not what they expected.

Meanwhile, someone else follows what looks like the exact same approach and loses weight, feels better and sees their blood markers improve.

So what is going on? Are diets simply good or bad?

Or is there something else happening inside each of us?

I think this is where we need to start looking at nutrition differently. Because the future of nutrition is not necessarily about finding the best diet for everyone. It may be about finding the right diet for you.

There is no single way your body responds to food.

Let's take a very simple example.

Two people eat the same meal. Same rice. Same dal. Same vegetables. Same portion.

You might assume that their bodies will respond in roughly the same way. But that isn't necessarily what happens. Their blood glucose response can be different. Their insulin response can be different. Their triglyceride response can be different.

Even their appetite and how long they stay full can be different. This is one of the things that has made personalized nutrition so interesting.

In the PREDICT 1 study, researchers gave more than 1,000 people the same meals and measured their responses. They found substantial differences between individuals in post-meal glucose, insulin and triglyceride responses.

In fact, the researchers found that the variation between people could be quite large even when they were eating the same food.

Think about what that means. The food on your plate may be exactly the same as the food on my plate. But my body and your body may not experience that meal in exactly the same way. And that is where the idea of personalized nutrition starts becoming much more interesting.

So why are our responses different?

There isn't one single answer.

• Your genetics play a role.

• Your age matters.

• Your body composition matters.

• Your physical activity matters.

• Your sleep matters.

• Your existing metabolic health matters.

• Your medications can matter.

And then there is something we are learning much more about today:

Your gut microbiome.

Your gut contains trillions of microorganisms, and the composition of that microbial community differs from person to person.

Researchers studying the PREDICT cohort found that the gut microbiome was associated with differences in metabolic responses to food. They also found that the relationship between diet, the microbiome and metabolism is complex and highly individual.

And this is important because it tells us something. You are not simply eating food and getting calories in return. Your body is processing that food through a biological system that is uniquely yours.

That doesn't mean every food affects every person completely differently.

There are still basic principles of nutrition that apply to all of us.

Vegetables are still vegetables.

Excessive added sugar is still something we should be careful about.

Protein is still important.

Fiber is still important.

Eating a diet based heavily on minimally processed, nutrient-dense foods is still a very good foundation.

Personalized nutrition does not throw all of that out. 

It asks a different question.

Once we get the basics right, how do we make the diet work better for the individual? This is where the “same diet” problem comes in.

Let's say I give 10 people the same 1,500-calorie diet. 

On paper, it looks perfect. 

• The calories are calculated.

• The protein is calculated.

• The carbohydrates and fats are balanced.

• The meals are nutritionally sound.

But does that mean all 10 people will get the same result?

Not necessarily. One person may find the diet very easy to follow.

Another may be constantly hungry.

One may feel energetic. Another may feel tired during training.

One may see their blood glucose improve significantly. Another may need a different distribution of carbohydrates across the day.

One person may enjoy eating the foods on the plan. Another may hate them and eventually stop following the diet altogether.

And this is something I think we underestimate.

A diet is only useful if the person can actually live with it.

Personalization is not just about your genes.

When people hear the words “personalized nutrition”, they sometimes imagine an expensive genetic test that tells them exactly what they should eat. That is not how I would look at it. Your DNA is only one piece of the puzzle. Personalized nutrition should begin with understanding the person sitting in front of you.

• What do they normally eat?

• What is their lifestyle like?

• What time do they wake up?

• When do they work?

• When do they exercise?

• How much do they sleep?

• What foods do they enjoy?

• What foods do they dislike?

• What is their medical history?

• What medications are they taking?

• What are their blood markers telling us?

• What is their body composition?

• What are they actually trying to achieve?

And perhaps most importantly:

What can they realistically sustain? 

Because there is no point designing the most scientifically perfect diet in the world if the person cannot follow it for more than two weeks.

And if you're wondering where your own diet stands, this is a good place to start. You can fill out the form below to get a personalised diet plan based on your goals and nutritional needs.

Get Your Personalised Diet Plan: click here

Your culture matters too. 

This is particularly important when we talk about nutrition in India.

A diet plan designed for someone in another country may be perfectly healthy, but that doesn't automatically make it the right diet for an Indian household.

Food is not just nutrition. Food is culture. It is family. It is routine. It is convenience. It is affordability. It is taste.

It is sometimes the difference between a diet that someone follows and one that they abandon.

For one person, breakfast might be eggs and toast. For another, it might be idli and sambar.

Someone else may prefer poha. Another person may eat dosa.

There is no reason personalized nutrition should mean abandoning the foods you grew up eating.

The question is how we build a nutritionally appropriate diet around the foods that actually fit your life.

That is a much more practical way of thinking about personalization.

But does personalized nutrition actually work better?

This is where we need to be careful.

Because personalized nutrition is an exciting area of research, but we should not turn it into another marketing buzzword. There is growing evidence that people respond differently to foods and that individual factors can help explain some of those differences.

But we are still learning exactly how much personalization improves long-term health outcomes.

A 2024 randomized controlled trial published in Nature Medicine compared a personalized dietary programme with general dietary advice. The personalized programme considered factors including individual post-meal glucose and triglyceride responses, food characteristics, microbiome information and health history.

After 18 weeks, the personalized approach produced improvements in several cardiometabolic measures compared with the control approach.

That is encouraging.

But I would still not tell someone that they need a microbiome test or an AI-generated food score before they can eat healthy.

We are not there. And we don't need to be.

Start with the basics, then personalize. 

This is probably the most important point I would make. Personalized nutrition does not mean that everyone needs a completely different set of foods. There are certain foundations that are remarkably consistent.

• Eat a variety of whole and minimally processed foods.

• Get enough protein.

• Eat enough fiber.

• Include vegetables and fruits.

• Choose healthy sources of fats.

• Stay within an appropriate calorie range for your goal.

• Stay physically active.

• Get enough sleep.

Then we start asking:

What does this person specifically need?

The American Diabetes Association's 2026 Standards of Care make a similar point. They state that there is no single ideal distribution of carbohydrates, protein and fat for everyone with diabetes, and that meal planning should be based on individual eating patterns, preferences and metabolic goals.

That is an important shift.

Instead of asking: “What percentage of my diet should come from carbohydrates?” 

We should sometimes be asking: “What amount and distribution of carbohydrates works for this particular person, given their health, lifestyle and goals?” 

That is a much better question.

Your body can change too.

There is another reason I don't like rigid diets. You are not the same person throughout your life. The diet that worked for you at 25 may not be the diet that works for you at 45.

• Your activity may change.

• Your muscle mass may change.

• Your sleep may change.

• Your work schedule may change.

• Your metabolic health may change.

• Your goals may change.

Even your appetite can change.

So personalized nutrition is not necessarily about finding one perfect diet and following it forever. It is about having a framework that can adapt as you do.

What if your diet isn't working? This is where I would ask you to stop blaming yourself immediately.

If a particular diet hasn't worked for you, it does not automatically mean you lack discipline.

• Maybe the calorie target was wrong for your needs.

• Maybe the food choices weren't sustainable.

• Maybe you were not getting enough protein or fiber.

• Maybe your sleep was poor.

• Maybe your activity level was different from what the diet assumed.

• Maybe there was an underlying metabolic or medical issue that needed attention.

Or maybe the diet simply wasn't designed around your life.

Before throwing the diet away and jumping onto the next trend, ask a better question: What isn't working, and why? 

That is where nutrition becomes less about following rules and more about understanding your body.

The future is not “one diet fits all”

I think we are moving away from the idea that there is one perfect diet that everyone needs to follow. But I also don't think the answer is that every person needs a completely unique diet made up of completely different foods.

The truth is somewhere in between.

We have common nutritional principles. And then we have individual requirements. 

The science is beginning to give us better tools to understand those differences. We are learning more about the microbiome. We are learning more about post-meal glucose and triglyceride responses. We are learning more about how genetics, lifestyle and metabolic health interact with diet.

And newer research is beginning to examine these relationships in much larger populations. A 2026 Nature Medicine study involving more than 10,000 people found strong associations between diet and the composition and function of the gut microbiome, further highlighting how individual dietary patterns and microbiome characteristics can interact.

But I think the biggest change is not going to come from technology alone.

It is going to come from asking better questions.

Instead of: “What is the best diet?” 

We start asking: “What is the best diet for this person, at this point in their life, for this particular goal?” 

That is a very different way of thinking about nutrition. And it is one that I believe makes much more sense. 

Because nutrition should not be about forcing yourself into somebody else's diet.

It should be about understanding what your body needs, what your lifestyle allows, and what you can realistically sustain. The same diet can work brilliantly for one person and fail completely for another. That does not necessarily mean the diet was good for one person and bad for the other.

It may simply mean that the person was different. 

And that, to me, is where the future of nutrition is heading.

Not towards more complicated diets. But towards more appropriate ones.

If you feel like you have tried every diet and still cannot figure out what actually works for you, this is where personalized nutrition can help.

Your calorie, protein, carbohydrate, fiber and micronutrient requirements are not necessarily the same as someone else's. A qualified dietitian or nutritionist can look at your health, lifestyle, food preferences, goals and nutritional needs and help build a plan around you, rather than asking you to fit into a generic diet.

Start Your Personalised Diet Plan: click here

Because the goal is not to find the diet that works for everyone. The goal is to find the diet that works for you.