Why No Diet Can Be Absolute?

Especially When You Have a Chronic Condition

Here, “absolute” means believing a food rule is always true, no matter who the person is or what their health condition, lifestyle, or eating pattern looks like.

For example:

• “Nobody with diabetes should eat rice.”

• "Don't eat rice — your sugar will shoot up."

• "Eat raw turmeric every morning — your thyroid will improve."

• "Avoid all fruit. Fruit has sugar."

• “This food will fix thyroid problems.”

These statements sound simple, but the body does not work that simply. The same food can affect two people very differently.

These kinds of statements travel fast — through family groups, clinic waiting rooms, YouTube videos, and well-meaning neighbours. They sound authoritative. They are stated with complete confidence. And they share one common problem: they treat the human body as though it is a uniform machine that responds the same way to the same inputs, in every person, every time.

It does not. And understanding why is one of the more practically useful things a person managing diabetes, thyroid disease, or any chronic condition can learn.

Two people. The same meal. Completely different blood sugar responses.

In 2015, researchers at the Weizmann Institute of Science conducted one of the most striking nutrition studies of the last decade. They continuously monitored blood sugar levels in 800 people over a week, tracking nearly 47,000 meals. Every participant wore a continuous glucose monitor. The researchers could see, in real time, how each person's body responded to what they ate.

The results were startling. People showed vastly different blood sugar responses to identical foods. One participant's blood sugar rose sharply after eating a banana but barely moved after eating a cookie with the same number of calories. For another participant, the exact opposite occurred. Some people had high blood sugar responses to bread but not to sushi. Others had higher responses to bread with butter than to plain bread alone — counter to everything conventional dietary wisdom would predict.

The researchers concluded that the glycemic index — the standard tool used to classify foods as "safe" or "risky" for blood sugar — is not a fixed property of a food. It is a property of a food in a specific person's body. And that body is shaped by things no blanket dietary rule can account for.

Why bodies respond differently to the same food

Several layers of biology explain this individual variation, and each one makes the case for why absolute dietary rules cannot hold across all people.

Gut microbiome. The trillions of bacteria living in the digestive tract are unique to each individual — shaped by genetics, childhood diet, antibiotic history, environment, and dozens of other factors. These bacteria influence how food is broken down, how much glucose is absorbed, how quickly the gut empties, and even how insulin sensitive the body is. Two people eating the same dal or the same chapati will have different microbial responses to that meal, producing different metabolic outcomes. Precision nutrition research increasingly shows that the gut microbiome is one of the primary reasons the same food affects different people differently.

Genetics. Nutrigenomics — the study of how genes interact with diet — has established that genetic variants affect how individuals metabolise carbohydrates, fats, and proteins. Some people have genetic variants that make them more efficient at processing certain starches. Others have variants that increase their postprandial glucose response to foods that cause minimal rise in most people. Genetics accounts for a meaningful portion of individual variation in how food is processed — though not all of it.

Insulin sensitivity and metabolic state. A person who is insulin resistant processes glucose from the same meal differently than someone who is insulin sensitive. A person who just exercised has more receptive muscle tissue for glucose uptake than someone who has been sedentary. Time of day, sleep the night before, stress levels, and recent illness all shift the metabolic context in which food is eaten — meaning the same food, eaten by the same person, can produce different results on different days.

Medication and disease stage. A person with well-controlled Type 2 diabetes on metformin will respond differently to a bowl of poha than someone newly diagnosed and medication-naive, or someone on insulin. A person with subclinical hypothyroidism and a slightly elevated TSH will have a different metabolic baseline than someone with overt hypothyroidism on levothyroxine. The disease context changes the dietary equation entirely.

Why "eat this, cure that" doesn't hold

The specific claims deserve addressing directly — not to dismiss the role of diet, which is real and significant, but to clarify what diet can and cannot do.

"Avoid rice and your diabetes will be controlled." Rice consumption affects blood sugar — but how much, and in what direction, depends on the variety of rice, how it is cooked, what it is eaten with, in what quantity, at what time of day, and in whose body. Research consistently shows that the glycaemic impact of rice in Indian meals is significantly moderated by the presence of dal, vegetables, curd, and fat in the same meal. Removing rice entirely while continuing to eat refined flour, sugar-laden snacks, and processed foods will not achieve what the blanket rule implies. And for someone who is physically active, has good insulin sensitivity, and eats modest portions, rice may be a complete non-issue.

"Eat this superfood and your thyroid will improve." Thyroid function is regulated by a complex hormonal feedback system involving the hypothalamus, pituitary, and thyroid gland itself. Foods rich in iodine support thyroid hormone production in populations where iodine deficiency is the underlying cause of dysfunction — which in urban India, where iodised salt is widely used, is increasingly not the primary driver. The more common cause of hypothyroidism in India today is Hashimoto's thyroiditis — an autoimmune condition that no specific food treats. Dietary modifications can support overall metabolic health and reduce inflammation, which matters. But the idea that a specific food will correct a hormonal or autoimmune condition is a significant overstatement.

"Don't eat fruit — it has sugar." Whole fruit contains fibre, water, micronutrients, and polyphenols alongside its natural sugars. The fibre slows digestion and moderates the glucose response. Study after study has found that whole fruit consumption is not associated with worsening glycaemic control in people with Type 2 diabetes when eaten in sensible portions — and is associated with reduced cardiovascular risk. Fruit juice is a different matter. But treating an orange or a guava as equivalent to a sweetened drink because both contain sugar ignores how food actually works in the body.

What diet actually is

Diet is not a prescription pad with fixed cause-and-effect relationships. It is a collection of inputs into a biological system that is already complex, already individualised, and already responding to a dozen other variables simultaneously. This does not mean dietary choices are unimportant — they are enormously important, particularly in conditions like diabetes and thyroid disease. But the impact of those choices is contextual, not absolute.

What matters is the overall pattern over time — the balance of food quality, portion appropriateness, meal composition, and consistency — rather than whether a specific food was eaten or avoided on a specific day.

The body is not a simple equation. Feeding it well requires understanding that — and being appropriately sceptical of anyone who tells you otherwise with complete certainty.

Dietary guidance that is actually useful is specific to you — your metabolic profile, your condition, your medications, your lifestyle, and your food culture. A clinical conversation about what to eat is worth more than ten general rules. If you have been following strict food prohibitions based on your condition and are unsure whether they are grounded in evidence, bring them to your next consultation.