Obesity affects millions of people in Germany. Many struggle with elevated blood sugar, Insulin resistance or the risk of type 2 diabetes. Mostly it’s about calories, sugar or amount of fat. But researchers from the German Institute for Nutritional Research Potsdam-Rehbrücke (DIfE) are now showing: The timing of the meal also matters intervenes in metabolism.

In a controlled study with overweight men, the activity of central genes in fat tissue changed – simply because of whether fat was eaten in the morning or evening. The amount of calories remained the same. Nevertheless, the tissue reacted measurably – a proven connection between meal times and metabolism.

Two nutritional rhythms in direct comparison

The researchers studied 29 overweight men without diabetes. Each participant completed two four-week nutritional phases. There was a four-week break in between. This meant that each man could go through both variants – under identical conditions.

The energy supply remained constant. The distribution of nutrients throughout the day was also the same: 50 percent carbohydrates, 35 percent fat, 15 percent protein. The only thing that changed was the timing.

• Variant 1: Carbohydrates in the morning, fat in the evening
• Variant 2: Fat in the morning, carbohydrates in the evening

At three fixed times – morning, midday and early evening – doctors took samples from the subcutaneous fatty tissue. This made it possible to closely monitor how genes work throughout the day.

Over a thousand genes work every 24 hours

In adipose tissue, the team identified 1,386 genes with a clear daily rhythm. Almost every third of these genes responded to the changed meal sequence.

Striking: classic inflammation levels such as CRP remained stable in the blood. The reaction was limited to the fatty tissue. This suggests an early, local effect.

Fat in the morning strengthens insulin action

If, on the other hand, the fat was mainly eaten in the morning, the picture was more favorable. Two metrics for adipose tissue insulin sensitivity improved significantly.

The rQUICKI index increased measurably. The ratio of adiponectin to leptin was also more favorable. Both values ​​are considered markers for the responsiveness of fat cells to insulin.

At the same time, genes that are crucial for energy metabolism increased. These include processes such as the citrate cycle and oxidative phosphorylation. The fatty tissue worked metabolically more actively under this rhythm.

Olga Pivovarova-Ramich from the German Institute for Nutritional Research Potsdam-Rehbrücke classifies the results as follows: “Our results confirm initial findings that the shift in macronutrient distribution throughout the day measurably influences the metabolic processes in fatty tissue.” And she adds: “Late, high-fat meals could perhaps trigger unfavorable molecular processes that may promote long-term inflammation and metabolic problems.”

Internal programs are postponed by hours

It wasn’t just the level of gene activity that changed. For 62 genes, the time of their daily peak phase shifted – in some cases by up to four hours.

A key example is the PDK4 gene. It regulates whether the body burns sugar or fat. Depending on your eating rhythm, this program started sooner or later. IRS1, IRS2 and PCK1 also responded sensitively to the temporal shift.

The central body clock, however, remained stable. Classic clock genes in adipose tissue and the stress hormone cortisol showed no fundamental changes. The effects primarily affected metabolic and inflammatory pathways.

Why late fat can trigger processes

Adipose tissue is an active organ. It stores energy, produces hormones and influences the immune system. If a lot of fat is consumed in the evening, free fatty acids remain in the blood longer. This can trigger signals that put the tissue under stress.

The data found evidence of increased ceramide levels after high-fat meals in the afternoon. Ceramides are associated with insulin resistance and inflammatory processes. At the same time, certain messenger substances such as leptin were higher.

Such changes occur early. You don’t have to get sick right away. However, in the long term they can promote conditions that play a role in obesity and type 2 diabetes.

Only men without manifest diabetes were examined. Statements about women or people with existing metabolic diseases are not possible. Long-term disease progression was also not examined.