What should we really avoid at the table, what is harmful for our metabolism?
We know that if we eat more than our caloric needs we gain weight, but beyond that, are there any foods to avoid to speed up the metabolism?

Yes. Those processed industrially, which in English are called “processed foods” are definitely foods to avoid more than a nice steak, more than butter or a bowl of pistachios.

If the rule of “don’t overdo it!” Applies to every food, with industrially processed foods the damage begins at the first bite. Additives including flavors, preservatives, dyes, substances that increase taste and flavor.

The problem, on the other hand, are those chemical treatments that are increasingly part of the agri-food transformation process.
There is a difference between carrageenan in industrial form that you find as a thickener and natural carrageenan which is a very banal seaweed.

Obviously, not all agri-food processing is harmful in our diet (think of wine, cheeses, pasta, oil: all foods obtained from raw materials with now industrial processes, not in the past), as much as that sector of agri-food processing that produces a new product, for example biscuits made from eggs, sugar and flour, or the spreadable cream from cheeses with melting salts. Or microwave popcorn from regular corn.

In these products we find dyes, preservatives, stabilizers, agglomerants, sweeteners, emulsifiers, acidity regulators and so on, as well as some manufacturing processes (lyophilization for example).

A spreadable cheese is more harmful than a slice of Camembert.
A slice of ham with polyphosphates is more harmful than a piece of cut of beef.

As revealed in this beautiful article by Dr. Biancamaria Saetta , nutritionist biologist:

Some studies show that the average body weight of humans has remained essentially stable for thousands of years. Suddenly in the sixties something changed and the populations of rich countries began to gain weight

What then would be the foods to avoid to avoid metabolic disorders and excess weight?

FOODS TO AVOID TO ACCELERATE METABOLISM

• Foods subjected to “food sophistication”: croquettes, soups, biscuits, spoon creams, everything that has a list of ingredients that you do not fully understand, made up of acronyms, nomenclatures and chemicals that you do not know what they are and what the hell they are for. The famous example of the oncologist Franco Berrino about the great-grandmother (or any very old woman, come on) is always valid. Take your great-grandmother with you to the supermarket, and for everything you put in your cart, have her read the ingredient list. If your great grandmother doesn’t know what those ingredients are, don’t buy those products.
• All foods preserved in non-BPA free plastics and films, in cans without coating, in metal cans. They can contaminate food with heavy metals, while BPA is an endocrine disruptor recently linked to obesity.
• Polyunsaturated fats are not from fresh and seasonal products. They come from industrial sunflower oils (ok high oleic sunflower), corn, safflower, cottonseed, rapeseed, soybean oils. These oils oxidize easily and thus produce free radicals. In addition, omega6, if in excess, promote the production of inflammatory substances such as thromboxanes.