Different things work for different people. According to a BBC article
, there is a genetic part. For some people, low-carb diets are best, for some people low-fat diets are best, and for some people a balanced diet works. Try each and see what works.
My experience has been that there are some things which are universal. It is ALWAYS good to increase the fraction of your calories coming from protein and to drink more water (at least 2 quarts/liters daily). Protein is more filling for its calories and digests fairly slowly, filling you longer. Water helps fill you up and speeds metabolism. Simple sugars don't fill you up at all, relative to their calories, and should be replaced with artificial sweeteners when possible. Some people find that eating extra fiber (beans, green vegetables) helps them feel fuller over time.
In the end, your wife is wrong: low-carb diets are NOT a universal solution. As long as you are eating significantly less calories than your body burns, you will lose weight. Choosing the mix of fat/starch/protein in your diet is a matter of personal preference: whatever keeps you happiest for the same calories is the best diet.
Edit: specific advice on diet
I'm really only eating Salad, nuts, boiled eggs, meat+salad sandwiches (on whole wheat bread) and then some meat + veg for tea.
Nuts are delicious, but they have a lot of fat and calories for their size; if they are a major part of your diet, you might feel fuller by swapping them out for the equivalent in protein calories. Boiled eggs and eggs in general are a great way to get cheap protein, and are pretty filling, can't argue with that. Milk is cheap and filling too, with a lot of protein. While I love bread, I find it is not a very satisfying meal for its calories.
You may not have enough bulk in your diet if your main veggies are in salads. You can add bulk without adding fiber by eating more green vegetables. I find salads boring as heck, so I like to do stir-fry with veggies and meat or mushrooms. Soups and satays are good ways to work in vegetables too. Or, if you're set on sandwiches, PILE them with tomatoes, spinach leaves, and onions. Onions are basically freebies for nutrition.
If you're in Britain, learn to cook a good saag with fresh spinach. Delicious and low-calorie if you omit or reduce the desi ghee/butter/cream.