Where to pay attention to when preparing a low carbon diet. And does it lead to lower CO2-emissions?:
Buy local products (?)
Local means often less kilometers. That means less fuel consumption, less pollution and less energy use in the transport phase as well as for preservation. Look at vegetables and fruit to the country of origin. However, if you value a fair economic distribution, this can be more important to you. It differs per person. It then might be useful in your trade off to know what share of total energy transport has for of a specific product. In practice, it is difficult as a consumer to be able to get a good view here. Roughly: by boat is ok, per plane is not advisable.
Choose seasonal food
There's a lot of energy needed for vegetables and fruit that are offered out of season. They are either imported from far or they are grown in heated greenhouses. Therefore they also are more expensive. Calendar: http:/www.groentekalender.be
Buy less greenhouse products (OK, if energy saving measures were taken)
Products from greenhouses are often difficult to recognize. For many products, however, can be concluded that they are out of the warm greenhouse. For example, in the Netherlands grown fruit vegetables like bell peppers, tomato, cucumber and eggplant almost always from heated greenhouses. In autumn and spring are also many other Dutch products from the heated greenhouse coming because it is too cold here to grow in the open ground. 
Use your garden
Vegetables, fruits and herbs from our own garden do not need to be treated nor transported.
Go to the producer
You can also buy your vegetables (and other products) directly on the farm, on the (bio) market or through a farm box subscription. Of course by bike.
Groceries as little as possible by car
Reports indicate , that a boat oranges from South-America is less harmful per orange, then the drive by car with which the orange is then bought at the store.
If you still want exotic products, choose fair trade. The products must be imported by ship, which pollutes less than the plane.
Choose products in bulk or larger packs. Even better are reusable packaging. Always take a backpack and/or shopping bag to your work, containing blank bread bags. That way you have never more vegetable bags or a plastic shopping bag. Friendly say "thanks, no bag" to all. You will notice how often you will do this.
Not too much processed
The purer the product, the less manufacturing and transport; even chopped onions for the stew go back and forth to Poland!
Potatoes instead of rice
During the hot meal Dutch people eat less and less potatoes and more pasta and rice. The energy and space of these foods increases in the order potatoes-pasta-rice. By replacing rice with pasta or a product like couscous, or best by eating potatoes more often, energy and space can be saved easily. Furthermore potatoes are an important source of vitamin B1 and vitamin c. Pasta and rice deliver less vitamin B1 and no vitamin C.
Use your oven less
Consider cold salad (from open ground vegetable) instead of heated vegetable. Limit long cooking in the oven.
Eat less meat (chicken is OK)
Meat is an inefficient source of protein. The amount of animal feed needed to produce the meat is a multiple of the amount of "vegetable people feed" (having the same amount of nutritional value). With 4 kilo of vegetable protein (animal feed) you produce on average only 1 kilo of animal protein. 
Eat less red meat and cheese
Bij rundvlees speelt de uitstoot van het sterke broeikasgas methaan (23 keer zo sterk als CO2) een grote rol als het gaat om uitstoot. Methaan komt vrij bij pensfermentatie (herkauwen). Dit zorgt bij koeien op gras voor 40% tot 75% van de broeikasgas-uitstoot. Technisch is het mogelijk om methaangas te verwijderen uit stallucht, maar economisch kan het voorlopig nog niet uit. (Agripress 2012)
Throw away as little as possible
 See Foodmiles
 Gerbens-Leenes, P.W. GroenKookboek. Groningen: RuG, 2000
 Šebek, L., E. Temme. De humane eiwitbehoefte en eiwitconsumptie en de omzetting van plantaardig eiwit naar dierlijk eiwit. Wageningen: WUR, 2009. p.17.  T. Ponsioen, R. Broekema, H. Blonk, Koeien op gras, 2010. p.9, p.39, p.44