Flaxseed itself hasn't been clinically proven to aid in weight loss. Most people who experience weight loss after adding flaxseed into their diet are experiencing that weight-loss because they are making broader changes to their diet that encourage healthier eating.

That said, flaxseed is a healthy addition to your diet. It is high in fiber, as well as lignans and ALA -- an Omega-3 Fatty Acid. Omega 3s have been clinically shown to help reduce cholesterol, improve cardio-vascular health, decrease blood pressure and reduce inflammation naturally. Flaxseed is a good option for vegans who want to increase their intake of Omega-3 but choose not to eat fish or take fish oil supplements.

Even though flax is high in ALA -- it's important to know that the body still needs to break that ALA down into to other Omega 3 fatty acids: DHA and EPA. The body doesn't do this very efficiently, so if possible, it's good to supplement with fish oil in addition to the flax, which is naturally high in both DHA and EPA.

In terms of the best form of flaxseed, I would recommend ground flaxseed meal, which is better digested by the body. Whole flaxseeds have a tendency to pass through the digestive system, which means that you won't get the full health benefits of the endosperm (the oily part of the flaxseed that is within the hard outer hull.) Keep the meal in the fridge or freezer, since once the seed is ground it can go rancid quickly.

Whole flaxseeds are best used on baked goods and breads, where the meal wouldn't work as well. It's easy to add some flax into your diet, just add a tbs of flaxseed meal in your morning oatmeal, granola, yogurt, cereal, smoothie, etc. 

Best of luck!