A low-fat, low-carb diet restricts both of the body’s primary fuel sources, leaving protein as the dominant macronutrient. This approach limits carbohydrates to roughly 130 grams per day or less (under 26% of calories) while also keeping fat intake well below the typical range, generally under 30% of calories. The result is a diet built heavily around lean proteins, non-starchy vegetables, and careful portion control of both grains and oils.
This combination is unusual because most popular diets cut one or the other. Low-carb diets like keto replace carbs with fat (70-80% of calories from fat). Low-fat diets allow plenty of whole grains and fruit. Cutting both at once creates a narrower set of food choices and raises important questions about sustainability, nutrition, and whether the trade-offs are worth it.
How It Differs From Keto and Other Diets
The easiest way to understand a low-fat, low-carb diet is to compare it to its cousins. A ketogenic diet restricts carbs to just 20-50 grams per day but encourages you to get 70-80% of your energy from fat. That high fat intake is what triggers ketosis, the metabolic state where your body burns fat and produces ketones for fuel. A standard low-fat diet, by contrast, keeps fat under 30% of calories but allows carbohydrates to make up 45-65% of your intake.
A low-fat, low-carb diet sits in neither camp. By restricting both macronutrients, protein necessarily fills the gap. You might end up eating 35-50% of your calories from protein, with the remainder split between modest amounts of carbs and fat. This makes it functionally a high-protein diet with dual restrictions on the other two macronutrients.
What You Actually Eat
The food list for this approach centers on lean protein sources. A 3-ounce serving of roasted white-meat chicken has 23 grams of protein, zero carbs, and under 1 gram of saturated fat. Baked salmon offers about 21 grams of protein with 1.7 grams of saturated fat. Dark-meat chicken, white fish, egg whites, and low-fat dairy round out the protein options.
For carbohydrates, the focus shifts to non-starchy vegetables like leafy greens, broccoli, bell peppers, and zucchini, which provide fiber and micronutrients with minimal carb load. Small portions of berries or legumes might fit depending on your specific targets. What gets eliminated or sharply reduced is a long list: bread, pasta, rice, potatoes, most fruit, cooking oils, butter, nuts, cheese, avocado, and fatty cuts of meat.
How Your Body Responds
When carbohydrates drop significantly, your body shifts its fuel source from glucose to a greater reliance on fatty acids and ketones. This metabolic shift is associated with reduced appetite, which partly explains why people lose weight on carb-restricted diets even without counting calories. However, when fat is also limited, the body has less dietary fat available to burn and must rely more heavily on stored body fat and protein for energy.
Your brain typically needs about 130 grams of carbohydrates per day to meet its energy demands through glucose alone. Below that threshold, the brain adapts by using ketones as a partial fuel source. This adaptation takes several days, and during the transition many people experience fatigue, brain fog, and irritability, sometimes called the “low-carb flu.”
Weight Loss: What the Evidence Shows
A meta-analysis of 23 randomized controlled trials comparing low-carb and low-fat diets found that both produced meaningful weight loss. Low-carb dieters lost an average of 6.1 kg (about 13.4 pounds), while low-fat dieters lost 5.0 kg (about 11 pounds). The difference of roughly 1 kg between the two approaches was not statistically significant, meaning the advantage of one over the other could be due to chance.
Low-carb diets did show a clear edge in some metabolic markers. Triglycerides dropped nearly twice as much on low-carb diets compared to low-fat diets, and HDL cholesterol (the protective kind) improved more. Low-fat diets, on the other hand, produced bigger reductions in total cholesterol and LDL cholesterol. Both approaches lowered fasting blood sugar by similar amounts.
Combining both restrictions into a single diet hasn’t been studied as extensively as either approach alone. The theoretical benefit is that you’d get the metabolic advantages of carb restriction while also limiting saturated fat intake. The practical challenge is that the more foods you eliminate, the harder the diet is to maintain.
Satiety and Sticking With It
One of the biggest concerns with restricting both fat and carbs is hunger. Fat and fiber are the two nutrients most responsible for making you feel full after a meal. Cut both, and you risk constant hunger that eventually derails the diet.
A year-long randomized trial of 148 adults compared appetite on a low-carb diet (under 40 grams of carbs per day) versus a low-fat diet (under 30% of calories from fat). The low-carb group preserved higher levels of peptide YY, a hormone that signals fullness to the brain. There was no difference in ghrelin, the “hunger hormone,” between the two groups, and self-reported appetite was similar. About 80% of participants in both groups completed the full year, suggesting that neither approach was dramatically harder to stick with than the other.
The catch is that this trial compared low-carb to low-fat, not a diet that restricts both simultaneously. If low-carb diets maintain satiety partly because of their higher fat content, removing that fat could undermine the appetite benefit. High protein intake does help with fullness, but whether it fully compensates for the loss of both fat and complex carbs is an open question.
Nutritional Risks to Watch For
Restricting both macronutrient groups shrinks your food variety, and that raises the risk of missing key nutrients. Research on low-carb diets has found that people tend to fall short on iron, calcium, thiamin (vitamin B1), and folate, largely because they’re cutting out whole grains, legumes, and certain fruits. These are the foods that provide the bulk of B vitamins and minerals in a typical diet.
Fat restriction adds another layer of concern. Your body cannot make two types of essential fatty acids on its own: omega-3 and omega-6. Males need about 1.6 grams of omega-3 and 17 grams of omega-6 daily, while females need about 1.1 grams and 12 grams respectively. These fats support hormone production, brain function, and inflammation regulation. On a very low-fat diet, hitting these minimums requires intentional choices like fatty fish, flaxseed, or targeted supplements.
Fat-soluble vitamins (A, D, E, and K) also need dietary fat to be absorbed properly. Studies on carb-restricted diets have observed moderate decreases in intake of these vitamins. When fat is also limited, absorption may drop further even if intake stays the same.
Who Might Benefit
Very-low-carbohydrate diets have the strongest evidence for people with type 2 diabetes, insulin resistance, or metabolic syndrome. These conditions involve impaired carbohydrate processing, and reducing carb intake directly addresses the underlying problem. Studies in people with type 2 diabetes following well-formulated very-low-carb diets have shown significant improvements in blood sugar control and disease markers.
Low-carb diets have also been used therapeutically for epilepsy since the 1920s and show preliminary benefits for polycystic ovary syndrome, cardiovascular risk factors, and certain neurological conditions. Adding a low-fat component on top of carb restriction is most commonly seen in short-term medical contexts, such as preparing for bariatric surgery or managing acute pancreatitis, where both restrictions serve a specific clinical purpose.
For general weight loss, the evidence suggests that the best diet is the one you can follow consistently. Both low-carb and low-fat approaches produce similar weight loss over time. Restricting both simultaneously may accelerate short-term results for some people, but the narrower food choices and potential nutrient gaps make it harder to sustain. If you choose this approach, prioritizing lean proteins, non-starchy vegetables, and a small amount of healthy fat (especially from fish and seeds) helps cover your essential nutrient needs while staying within both restrictions.