We're all different. If we are all on the same weight-loss diet, there will be various outcomes. Some people will lose a lot, some will lose a little, and a few will even gain weight.

Science still can't tell us why some people lose weight easier than others.

Scientists are continually finding links between genetics and nutrition. Many of us have a gene called FTO that makes us more likely to be overweight. You can get a genetic test to tell which variant of the FTO gene you happen to have.

However, scientists who study the genetics of nutrition think it’s premature to base nutritional advice on your DNA. That FTO gene, for example, has only been shown to make a few pounds’ difference in body weight.

The coded messages of your DNA are billions of letters (nucleotides) long. Personalized nutrition companies only care about a few of your DNA letters and can tell you which "variant" you have at each of those locations (known as SNPs) along your DNA strands.

Genetic testing companies can learn what SNP variants you have by supplying them with a vial of spit.

With some genetic testing products, you can view your results on a particular screen on the app. There are 19 results in total, with five relating specifically to weight loss.

Among other things, you can, for instance, learn about your Vitamin and mineral levels or exercise abilities.

DNA testing companies can interpret the data from the same sample differently because they use different SNPs to come to their conclusions.

Some might tell you how you will be able to lose weight, or how your diet will affect you. They can also make automatic recommendations to suit your diet and goals.

Regardless of how personalized your diet advice gets, your recommended diet will not be drastically different from what we all know to be healthy: more vegetables, more exercise, etc.

One study hoped to confirm that a specific combination of genes would determine whether people lost more weight on a low-carb or a low-fat diet. They found that the subjects' genetic profiles were not associated with their chances of success.

Although people buy genetic testing kits from companies to find out how to lose weight, the companies themselves acknowledge the limitations of the science and are careful to word their claims so that they don't outright promise weight loss.

Some researchers think that companies are overreaching when they use these types of studies and translate the data into prediction.

Genetics alone cannot explain why some people are fat and others thin. Other factors include what you do and what happens to you. What can be revealed with known genes is in the single digits.

• One 2015 study of 97 genetic variants known to affect body weight revealed that they could only explain less than 3% of person-to-person differences in MBI.
• Researchers are still not sure whether the FTO gene makes a protein that influences body weight.
• Many of the studies on genetics used people of European ancestry and cannot guarantee that the results will mean the same thing in other populations.