My contention is that the author is not to be trusted implicitly. He is not a nutritional scientist, nor has he done peer-reviewed research in the field. He could certainly earn my trust, and is not prevented in doing so by selling something. However, what he does sell is based upon a controversial nutritional concept which is not vetted by rigorous scientific research and directly conflicts with scientifically researched medical understanding of the human body. I don't trust him immediately because he sells something based upon this, though I don't begrudge him the right to sell products he believes in. I just don't have to buy them or ascribe to his philosophy.

As for his nutritional philosophy it is based on low-carb intake to reduce fatty tissue build up in the body. When I see a controlled well-designed study, I will be more apt to believe it. Until then, what I'm doing now is working just fine and I don't have to buy anything from someone who asks me to believe something that doesn't make sense outright to me and violates a lot of media literacy principles. The publisher has an explicit bias, it confirms something that you want to be true (that you can lose weight simply by changing the proportions of what you eat), and is literally just a re-hash of a fad diet from 15 years ago (the Atkins diet).

As well, do you really think that the optimal number of carbs for all people of varying shapes and sizes and genders just happens to be a round number like 100? How did this number happen?

Eating when you're hungry and not over-eating is standard advice so I agree with the premise, though here it's not really defined what either of those mean. What does hungry mean here? That my stomach growls, or that I thought of food and it was appetizing. Hungry is an adjective, not a metric. Overeating similarly has no explicit limit, so it as well seems designed to make the whole idea very palatable and easy to manage, while simultaneously not providing any gauge for success.

On the other hand, let's look at my simple, not selling you anything advice.

If you are simply trying to lose weight, you just have to eat less than you burn.

You burn calories at a given amount just by going through your daily activities. This is called your Basal Metabolic Rate (BMR).

You do not have to exercise to lose weight, as long as you are eating less than your BMR. The rate at which you lose weight is directly related to how much less you eat than your BMR.

You can safely eat 1000 calories less than your daily BMR, as this will lead to a 2 lb. per week weight loss which is considered healthy by nutritional scientists, but a 500 calories deficit is easier to manage in longer durations so you may lose less in the long run.

When you are cutting it is a good idea to take a multivitamin to make sure that the vitamins and minerals from the food you usually eat are still being maintained at healthy levels.

Eating foods which are high in insoluble fiber will make you feel fuller and make caloric restriction easier. Insoluble fiber is found in the skins of fruits and vegetables, nuts, whole grains, prunes, asparagus, corn and bran.

When you are at the weight you would like to maintain, simply eat at your BMR (which gets smaller as you lose weight because a lighter body has less mass to maintain and feed).

This got really long but it's important.