You have been eating more balanced for a few days: when can you really feel a difference? Some signals may appear quicklybut biological markers and lasting benefits are built over weeks, months or years.
In “The advice of Doctor Kierzek”, broadcast on ICI on November 5, 2026, the emergency doctor offers a concrete chronology, without miracle promises.
Possible effects from the first days, but not acquired for everyone
To help understand, Dr. Kierzek compares dietary change to a garden: some seeds grow quickly, while protective trees take time. It also presents the intestinal microbiota as the “living soil” of this interior garden. The image speaks for itself, but it should not be read as an individual guarantee.
In a publication by David LA et al. In Nature
in 2014, a very marked dietary change rapidly modified the composition and activity of the microbiota, with differences observed from the first day in adults. This does not mean that lasting benefit is acquired in two daysbut the intestine can react quickly.
The first points to remember are simple:
- In 24 to 48 hoursthe microbiota can already react to a significant dietary change;
- In a few days, some people experience a more regular transit if fiber gradually increases and hydration follows;
- At the same time, reducing very heavy meals and limiting fast sugars can reduce afternoon fatigue in some people.
The key point remains progressiveness. A sudden increase in fiber can cause bloating or gas. To take care of your microbiota with varied fibers, it is better to take steps rather than transform your entire plate overnight.
Blood pressure, cholesterol, weight or morale: the benchmarks are counted in weeks then in years
After one to two weeks, Dr. Kierzek mentions a possible first effect on blood pressure with the DASH diet, rich in fruits, vegetables, whole grains and low in salt. This benchmark is consistent with the DASH trials, especially in people with high blood pressure at baseline. On the other hand,
a dietary change should never lead to stopping or modifying antihypertensive treatment without medical advice.
After 4 to 6 weeks, Dr. Kierzek also cites a possible drop in LDL cholesterol, especially with less saturated fat and more fiber, such as that of oats, legumes or fruits. “Portfolio diet” type work, including the essay by Jenkins DJA et al. published in
JAMA in 2003, measured changes in blood lipids over a few weeks. But these effects are verified by a blood testnot just by feeling. The idea also applies to blood sugar levels: meals can influence daily variations, while the overall balance can be judged with appropriate monitoring, particularly in the case of diabetes or treatment. On oats, it is better to keep a measured reading of the effect of oat fiber on LDL cholesterol.
For the skin, Dr Kierzek points out that it renews itself in about a month: a difference can therefore take a few weeks, without certainty, because the skin also depends on sleep, stress, hormones or care. For morale, he cites an Australian study: the SMILES trial by Jacka FN et al., published in
BMC Medicine in 2017, suggests that a Mediterranean-style diet, accompanied by a dietician, can improve depressive symptoms after 12 weeks in certain patients.
This approach remained complementary and did not replace treatment for depression.
In terms of weight, the doctor invites us to think in months and suggests a maximum rate of 0.5 to 1 kg per week. But he adds an essential nuance: the scale is not the only indicator. Blood pressure or cholesterol can improve without weight loss, which is also important for health.
To keep up, his advice is above all realistic additions, not a list of prohibitions:
- Add a vegetable to each meal;
- Replace the soda with water;
- Choose wholemeal bread rather than white bread;
- Introduce vegetables, legumes and fruits before eliminating foods;
- Keep an 80-20 logic, without feeling guilty after a friendly meal.
The most protective benefits are built over timeby repeated habits. In the event of chronic illness, pregnancy, eating disorder, cardiovascular or metabolic treatment, significant dietary changes must be adapted with a health professional.