AI tools such as Google Gemini and ChatGPT have taken the world by storm. More people are now turning to AI for everyday advice, particularly when it comes to health and wellbeing. In fact, healthy living, cooking guidance and medical advice were among the most searched AI topics in 2025.
As AI becomes more sophisticated, it's also changing the way people approach their diets. From generating meal plans to analysing nutritional needs, AI for nutrition and diet planning is becoming increasingly common. But while AI can provide quick answers, can it deliver truly personalised advice? And should it replace the expertise of a qualified nutritionist?
How AI is changing personalised nutrition
How AI is changing personalised nutrition goes far beyond chatbots. Calorie-tracking apps, smartwatches and even smart rings can monitor activity levels, heart rate, sleep quality and estimated calorie burn, creating a detailed picture of your daily habits. Combined with AI, these tools can recommend meals, suggest calorie targets and even tailor advice based on your goals, making AI for nutrition, training and weight management more accessible than ever.
However, relying solely on algorithms and data comes with risks. Without the knowledge of a qualified nutrition expert, AI can overlook important medical conditions and misinterpret nutritional research, resulting in advice that isn't appropriate for the individual.
Some of the biggest limitations include:
- Scientific gaps: Nutrition science is highly nuanced, and AI often oversimplifies or misinterprets conflicting research.
- False narratives: AI can generate convincing but incorrect nutritional advice, potentially leading to vitamin toxicities or nutrient deficiencies.
- Over-reliance on algorithms: Depending entirely on AI can reduce a person's ability to recognise natural hunger and fullness cues.
So, how accurate is AI when it comes to nutrition advice? And can AI for nutrition planning really provide the same level of personalised support as an experienced nutritionist?
To find out, Mark Gilbert, nutritionist at The 1:1 Diet, draws on more than 30 years of experience in nutrition and weight management to assess ChatGPT's responses to some of the most common questions about diet and healthy eating, before comparing them with his own expert recommendations.
The results show where AI can be a useful starting point and where expert nutritional guidance remains invaluable.
We asked, ‘How do I boost my immune system?’
ChatGPT said:
Your immune system works best when it is supported consistently rather than boosted quickly. A balanced diet with enough protein, fruit and vegetables helps provide key nutrients like vitamin C, zinc and antioxidants. Regular physical activity, staying hydrated and managing alcohol intake also play a role in keeping your immune defences working well.
Sleep and stress management are just as important. Poor sleep can weaken immune response over time, while chronic stress can make you more vulnerable to illness. Aim for steady routines, good sleep quality and regular movement rather than looking for quick fixes.
Mark’s commentary on response:
“This is a reasonable answer, particularly because it highlights vitamin C and zinc. However, vitamin D is more commonly lacking in many diets and is arguably more important for immune health. Some experts suggested during and after COVID that vitamin D3 supplementation may have reduced disease severity and potentially saved many lives. Vitamin A should also have been mentioned.”
We asked, ‘How much vitamin D do I need?’
ChatGPT said:
In the UK, the general recommendation is 10 micrograms (400 IU) per day, especially during autumn and winter when sunlight is limited. Vitamin D helps maintain healthy bones, teeth and immune function.
Most people get very little from sunlight during colder months, so supplementation is often advised. It is also found in foods like oily fish and fortified products, but diet alone is usually not enough to meet needs year-round.
Mark’s commentary on response:
“This answer is not very helpful because it gives a general recommended intake rather than explaining how someone can work out their individual vitamin D needs. This is particularly important in the UK, where standard recommendations may be too low for many people.
Ideally, people should have their vitamin D levels tested, as this is the only reliable way to understand their personal requirements. A level above 50 nmol/L is generally considered adequate, although some research and recommendations suggest that levels above 75 nmol/L may be preferable.
For people under 50, I and many experts I respect would recommend at least 25-50 micrograms (1000–2000 IU) of vitamin D per day. For those with levels below 25 nmol/L, I would suggest 100 micrograms (4000 IU) until levels rise to at least 50 nmol/L, and ideally closer to 75 nmol/L.
If someone does not know their vitamin D status, they should consider the time of year. In the UK, vitamin D is not produced from sun exposure during the five to six months before, during and after winter (October to early March), so I would generally recommend 50 micrograms (2000 IU) during this period. Less may be needed in summer if someone regularly spends time outdoors with skin exposed and without sunblock. People with naturally darker skin may need more vitamin D (up to three times more sun exposure), while those with lighter skin may need less.”
We asked, ‘How many calories should I eat to lose weight?’
ChatGPT said:
This depends on your age, size, activity level and metabolism. A common approach is to reduce your maintenance calories by around 300 to 500 calories per day, which typically leads to gradual fat loss.
For many people, this still allows enough energy for daily life and exercise. Tracking intake or working with general guidelines can help, but consistency matters more than perfection.
Mark’s commentary on response:
“This is a typical response, reflecting the way AI draws on broadly available information to identify perceived consensus. However, a 300 to 500 calorie deficit does not necessarily provide an optimal rate of weight loss.
It also may not produce sufficient weight loss to meaningfully improve metabolic health or reduce the risk of the most serious lifestyle-related diseases, including heart disease and certain cancers. This is supported by a large body of research, including the five-year follow-up data from participants in the DiRECT trial."
We asked, ‘What’s the best breakfast for weight loss?’
ChatGPT said:
A good breakfast for weight loss is one that keeps you full and stabilises energy levels. Protein is key, along with fibre, as both help reduce hunger later in the day.
Examples include yoghurt with fruit and oats, eggs with wholegrain toast or a protein-rich smoothie. The best option is one you can stick to consistently rather than something extreme or restrictive.
Mark’s commentary on response:
“Again, AI stays fairly surface level, picking up general examples from studies that suggest higher protein breakfasts can support satiety and weight loss compared with more refined, starchy options, but it doesn’t move into practical, optimised recommendations.
Eggs and yogurt are both strong choices for breakfast, but on their own many people will not reach a meaningful protein target. For best results in terms of fullness and appetite control, a minimum threshold of protein is needed from these higher quality sources. Yogurt also has added benefits, including calcium, and dairy fat intake has been associated in some research with lower risk of common lifestyle-related diseases.
A clearer guideline would be at least 20 grams of protein at breakfast, for example, three eggs or around 200 grams of high-protein Greek yoghurt. A smoothie containing 20 grams of quality protein alongside fruit would also be an effective option.”
We asked, ‘Can I lose weight just by exercising?’
ChatGPT said:
Exercise helps create a calorie deficit and improves overall health, but it is usually not enough on its own for significant weight loss. It is easier to consume calories than burn them through exercise alone.
Combining exercise with a controlled diet is more effective. Strength training and regular walking are particularly helpful because they support muscle maintenance and daily energy use.
Mark’s commentary on response:
“This isn’t a bad answer, although it would benefit from more specificity. Even with well-structured, closely monitored exercise programmes, studies typically show modest weight loss over several weeks or months, often around 5 pounds or less.
By contrast, research on The 1:1 Diet has shown substantially greater weight loss outcomes, with participants losing between over 1½ to over 3 stone in as little as eight weeks.”
We asked, ‘How important is sleep for weight loss?’
ChatGPT said:
Sleep plays a major role in weight regulation. Poor sleep can disrupt hunger hormones, making you feel hungrier and more likely to crave high calorie foods.
Consistently getting around seven to nine hours can improve appetite control, energy levels and training performance. Good sleep also makes it easier to stick to healthy habits long term.
Mark’s commentary on response:
“This answer is correct, though it could have gone further. Poor sleep can significantly disrupt blood glucose regulation, to the extent that in some cases it may produce readings similar to those seen in diabetes, with clear implications for appetite, energy balance and overall health.
It is also important to note that the relationship works both ways. Poor sleep can increase appetite and contribute to weight gain, while weight gain and overeating can in turn worsen sleep quality. This creates a cycle that can progressively impact both sleep and metabolic health.”
We asked, ‘Does stress affect my weight?’
ChatGPT said:
Yes, ongoing stress can influence weight through hormonal changes, particularly cortisol. This can increase appetite and make it more likely to store fat, especially around the abdomen.
Stress can also affect behaviour, leading to emotional eating or reduced motivation for exercise. Managing stress through routine, movement and downtime can support weight management.
Mark’s commentary on response:
"ChatGPT’s response is broadly accurate at a population level, but individual responses to stress vary, with some people eating less and losing weight when stressed. The evidence linking chronic stress to weight gain is mixed, although there is a slightly stronger association with abdominal fat in higher quality reviews, and the relationship is not consistent across individuals.
Cortisol rises during stress and may play a role in weight regulation, but it is only one factor among many and is difficult to measure reliably due to natural daily fluctuations. In practice, stress is more likely to influence weight indirectly through its impact on sleep, which has a clearer and more established link to weight gain."
We asked, ‘Are weight loss injections safe?’
ChatGPT said:
Weight loss injections can be effective for some people, particularly those with higher body weight or related health conditions. However, they are not suitable for everyone and must be prescribed and monitored by a medical professional.
They can also come with side effects such as nausea or digestive issues, and weight may return if lifestyle changes are not maintained. They work best as part of a broader approach rather than a standalone solution.
Mark’s commentary on response:
“This is a fairly generic, cautious response, but it does not fully reflect the breadth of safety information included in official prescribing guidance. There are well-documented warnings listed in regulatory product information, including a boxed warning regarding thyroid C-cell tumours observed in rodent studies, with relevance to humans still uncertain. These drugs are also contraindicated in patients with a personal or family history of medullary thyroid carcinoma or MEN 2, and patients should be advised to watch for symptoms such as neck lumps, hoarseness or swallowing difficulties.
Other important warnings include risks of pancreatitis, gallbladder disease, hypoglycaemia when used with insulin or sulfonylureas, acute kidney injury linked to dehydration, and significant gastrointestinal side effects. There are also cautions relating to diabetic retinopathy complications and monitoring for mood-related changes, alongside very common side effects such as nausea, diarrhoea, vomiting, constipation and reduced appetite, which are frequently reported across trials and real-world use.
Overall, gastrointestinal effects are the most common, with a substantial proportion of users experiencing some form of digestive symptom, and in some studies this has affected the majority of participants to varying degrees."
The summary: Can you trust AI for your nutrition planning?
AI can be useful for general nutrition information and simple guidance, but it often stays surface level and can miss important nuance in both research and real-world application. Much of the nutrition and health content that appears online does not always reflect the strongest available evidence, and AI systems can unintentionally amplify common but inaccurate beliefs because they draw heavily on what is most widely repeated rather than what is most reliable.
This can lead to responses that are incomplete or misleading, and a significant proportion may lack accuracy or depth, particularly where the evidence is complex or contested. AI also offers generic advice, despite the fact that nutritional needs vary from person to person, meaning individual requirements are not fully addressed. Overall, it works best as a starting point rather than a replacement for professional nutrition support.
For expert, in-person and tailored diet and nutrition advice from a Consultant trained by Mark himself, why not find a Consultant near you today?