Some MPs are being approached by lobbyists at least 100 times a week, a report by the Hansard Society says.
Lobbying is part of a healthy democracy, the report says
It reached this figure by asking 160 MPs about the number of approaches they received from charities, businesses, trade unions and public sector workers.
It says the lobbying industry is worth about £1.9bn a year and that lobbying is "symbolic of a healthy democracy".
But Labour MP Stephen Pound said that lobbying was "one of the most flagrant wastes of money in modern politics".
Many large organisations and industries use lobbyists - often former ministers or senior journalists - who have contacts with politicians and offer advice on how to influence policy. About 14,000 people are employed in the industry.
Critics argue this corrupts the system, putting private interests above those of voters.
The Hansard Society - whose stated aim is to "promote effective parliamentary democracy" - spoke to 81 Labour MPs, 55 Conservatives, 19 Liberal Democrats and five from other parties.
It found that 22% of MPs were contacted by interest groups at least 50 times a week and 59% at least 20 times.
Some 51% said they were lobbied at least 20 times a week by charities and 39% by businesses.
Meanwhile, 31% received this many approaches from public sector organisations and 22% from trade associations.
Adding all these figures together meant some politicians were being approached more than 100 times a week in total, the report said.
Of the MPs questioned, 61% said they were more likely to be persuaded by charities than companies.
But being spoken to by a constituent - rather than a professional lobbyist - had the greatest effect.
The Hansard Society said many people saw lobbying as "antithetical to democracy".
But it argued: "This direct or indirect lobbying of policy-makers and other stakeholders is widespread and deeply ingrained in our democratic system.
"Indeed it is symbolic of a healthy pluralist democracy."
The report added: "If lobbying, in its widest sense, did not produce commercial results and consequently improve profits, then it is reasonable to assume that it would not be carried out at all.
"Businesses make their investment in the expectation that they will see a worthwhile return and it is this interaction between the political process and profit that fuels scepticism about the role and influence of lobbying."
But Mr Pound, MP for Ealing North, said: "Every single day we get a blizzard of e-mails, a snowstorm of post.
"It's one of the most flagrant wastes of money in modern politics, mostly because MPs are contacted in a scattergun way, rather than with precision."
Mr Pound said MPs were far more likely to listen to interest groups than businesses and that constituents' demands were the priority.
The Hansard Society report is called Friend or Foe? Lobbying in British Democracy.